I know you're looking at SLR and have some lenses from other cameras. My previous film setup was a Cannon 35mm with four different lenses. Nothing super fancy, but all decent quality. I had a few thousand dollars in the setup as it was for my travels around the world in the Marine Corps, and then later on when I started to travel on hunting trips.
I have a few friends with Digital SLR's that they bought for the same reasons everyones mentioning here. They had the lenses already and they wanted to take advantage of them to use with a new digital camera.
I'm not a pro, don't have the best eye in the world and don't really care for one brand over another. I won't mention the brands they have as it's not important. They all seem to work the same. I will say that they spent quite a bit of money on those cameras!!
We went on a trip to Beavers Bend Oklahoma this past fall. The colors were amazing with cyrstal clear streams through the rock outcroppings. Just amazing. They loved thier pictures, but when compared to ours, it was kind of embarassing how dull there pictures were to ours.
Sometimes it's best to just take the hit, sell your old stuff for what you can get for it, and upgrade. I wouldn't buy an SLR again. The built in 12x optical zoom on the cannon is simply amazing. It's way more powerful than a 500mm zoom lense and it's already built in. No changing lenses or anything extra to carry around. It really does it all!!!!
If nothing else, be sure to at least go to a store and compare them. Try out a few brands and see the difference. Read the reviews and maybe try to find people with the cameras that interest you. That's what we did and ended up with the Cannon.
Good luck,
Eddie