I am most loyal to Canon because of my recent experiences. I have had the following Canons over the past few years: 300D (Digital Rebel), 20D, 30D, 5D, S400, S80. Why so many? I'm a wedding photographer.
When I started out, I got the Digital Rebel, which was a great learning tool. I still use it when I go scuba diving, because if the underwater case floods, I won't be too heartbroken.
The 20D and 30D are my most-used cameras now, because I have several EF-S lenses and those can't be mounted on the 5D. I love the 30D the most, but it's not that much better than the 20D really. My 20D and 30D come with me to all weddings.
I recently got the 5D and I love the quality and speed (for weddings anyway). I probably will end up loving this camera more than the others, but I am not familiar/comfortable enough with it to start using it as my main wedding camera. I also mentioned before that I have several EF-S lenses, so I have to invest in some more lenses for my 5D to make it more wedding-friendly.
My S400 died about a year ago after 3 years or so. I got several great photos from that little camera, and I am disappointed that I couldn't get it repaired (it cost too much to repair it, so I didn't bother).
My S80 was purchased to replace the S400. It's the best P&S I've ever used. It's a bit large, but it still fits in a pocket. It gives very sharp images and I take it everywhere (it lives in my work bag or my pocket).
Before I went digital, I used a Nikon N80 and F100 as a wedding assistant. Great cameras, but when it was time for me to become a pro, I decided to go Canon after doing about 9 months of research and trolling
http://www.dpreview.com. It was a tough decision and I don't bash Nikon, but I'm glad I went with Canon.