I have in film cameras a Nikon FM, FA, and F2 ( before those I has a honeywell pentax and a mamiya and the school cameras were minoltas ) and in Digital a D40 and a D300 so you can probably figure that I am going to say Nikon as my personal choice. I have friends that are just as loyal to Canon and I really cannot say anything bad about thier cameras either.
Realize whats right for me may not be right for you and I have friends who use Canon and love them and take great photos. I don't think any of the cameras you listed would disappoint you.
OK here is my short answer. for digital I have a Nikon D40 and I love it. The D40 has a full manual mode, Flexible progam, aperature priority, shutter priority modes. These are the same modes on all DSLR. It also has several other programed modes for things like portrait, night, children etc. As a photographer improves and learnds to use metering better these additional modes seldom get used so they are usually found on the more amature cameras and seen as not needed on the professional cameras. I feel I have a fair amount of experience as a photographer and it performs well for me but I can give it to my 12 y/o grandson if set on program and he can get good usable pictures as well. His photography is improving as he is already learning to use many of the functions himself ( yes I'm a proud granpa) .
I also would not get caught up in the megapixel hype and instead look at the entire sensor issue. Look at the article I linked below The D40 will do everything a beginner to intermediate photographer needs at a great price. It comes with an 18-55 lens. It will let you use any other money to buy more accessories. And by the time you outgrow it cameras will have advanced to the point that most of what is on the market now would be obsolete. I bought a D300 last year and only had a it a few months when the D700 came out. The canon would also serve you well but I am a Nikon person so I suggest them. I have friends that are very happy with thier canon's and take great photos. You will have others that like Pentax and Olympus and they are not bad cameras but if they were in the same ballpark you would see many more professional photographers use them
So get the D40 and spend the rest of your money on accessories
Enjoy whatever you get
Ted is right when he says "it is really the photographer who makes the image great." In that you can give the best camera in the world to a poor photographer and it will not give great images. On the other hand the example I use is to pick the greatest violinist in the world. Give him a 100 dollar violin and yes he will play it well. Next give him a stadavarius. I am willing to bet you right now he sounds better on the strad. So while a great camera will not the photographer make a poor camera can limit a photographer from reaching his potential
ADDED: Ok here is my longer answer to debate some concerns brought up in other answers
Now for the longer answer as you already have some experience I will be preaching to the choir on a good bit of this.
I would say the Nikon D40 Its an entry level DSLR. A digital SLR will give you a much larger sensor than any point and shoot camera. Larger sensor = more light to each pixel = clearer, crisper photo with better color saturation. DSLR will also let you grow and take more control as you learn more and you can change lenses when you have a need to. The sensor on the olympus is smaller than on Nikon or Canon
I am a nikon person and have had nikons since the 70's I personally think the nikon D40 give you more for the dollar than any DSLR today. There are some that do more but you pay a good bit more. Do not let the lower megapixels concern you if you do not do very very large prints you will never notice the lower DSLR. My brother recently needs a DSLR for a class and I recommended the D40 to him So I would also say get the D40 not the D40X. The Nikon D40 does not have limited functions compared with other entry DSLR. Yes it has fewer funtioncas than a 1500 dollar camera body would. It is not a a cut down version its equal or above most any entry level DSLR.
Some people will try to tell you there is little difference in output from a bridge camera ( or point and shoot ) and a dSLR.. dSLR will have at least an APSc sensor or larger. Larger sensor = more light per pixel. More light per pixel yields better color satureation, better dynamic range, better geometric accuracy and lower noise. In short better quality output.
I have a d300 and a d40 and when I am shooting for fun I grab the d40. Its weightless, a joy to use and gives good results
If you have a bit more money the D60 give you a number of things you want. It has newer firmware and image processors, designed for the 10 mp sensor. It has an "Active Dust Reduction System with Airflow Control ". Nikon not putting a system on the D40 to deal with dust is one of the biggest drawbacks I see to the D40 ( though I think its still a great camera for the money) If you change lenses dust will get in and the camera needs a system to deal with it. With the D60 you get a VR lens. That will help with low light situations ( they may offer that now with the D40 but originally it was not) . The D60 has Adaptive Dynamic Range. Nikon calls it "Active D-Lighting," it lets you save some highlights that my otherwise be lost. It has a newer better metering system than the D40. So you can get the D40 not the D40 x and spend the other money on lenses or a flash
Some people will want to make a big issue out of the fact that there are some nikon lenses that will not autofocus on these cameras. Right now there are "only" about 39 lenses that autofocus on these cameras. They cover the range of focal lengths. I doubt any photographer would be seriously limited with "only" this many lenses to choose from. If you want to manually focus you can more than double this and do so at a low cost. Manual focusing is easy and how we did things for decades before the advent of autofocus.
Cannon and Nikon chose to put the vibration reduction in the lens rather than the body. Somefolks put it in the camera and make of that. Yes that means you get stabilization only on lenses with that feature built in. In the body in theory it would work on every lens. But in fact image stbilization in the lens has proved to work faster and smoother with a lower impact on focus times than image stabilization in the body/ One problem with in body stabilization comes from the fact that the sensor would have to move different amounts for different focal lengths. A canon white paper says an in body system would have to move the sensor 1/4 inch to account for movement on a 300 mm lens.
Now a comment on liveview. Have you ever tried to hold several pounds of digital camera and lens steady at arms length while you look at an LCD screen. It not at all the same as holding a few ounces of point and shoot camera steady in the same position. One of the things we preach to new photogrpahers is to learn to hold the camera properly so the body mechanics give you a steady shot. You can't really do that looking at the LCD. So liveview is really something that will have very limited applications in a DSLR. . Usually only when its on a tripod. I have liveview on my D300 and have never used it.
Nikon also has great service. I was just reading the other day on eyefetch in the Nikon forum where someone posted that they had dropped thier lens and broken it. It was not a fault of the company they messed up. The sent it to Nikon and Nikon could not fix it. Nikon offered them a brand new identical lens at half the price. They did not have to
In closing all major camera manufactures make good cameras get out and compare the features and how they feel in your hand. Go to places like kenRockwell.com and DPreview.com to compare them. Nikon and Canon have the largest market share and I personally think there is a very good reason they do. Not bashing other brands but photographers tend to be very very demanding folks and they then tend to be loyal to what has worked for them well and consistently. That is not a pavlovian response anymore than it is a pavlovian response in my work at the fire department when I trust the brands of turnout gear and airpacks that have worked for me time and time again. Sometimes even going beyond the published specs. People in ANY demanding profession gain loyalty and trust from thier experiences. And if the product did not perform it would not be favored for long.