I just recently decided to upgrade my D-Reb to get access to some of the custom features (FEC, custom modes, mirror lock up) available in the next level of D-SLRs from Canon (10D/20D).
Having tried out the 5D, I can't say enough about it, but the coin involved in that purchase was out of my price range. I took a look at the 20D, but the difference in picture quality was not worth the jump in price from my D-Reb, and I am not a sports shooter, so the instant on feature that the 20D offers is not important to me. Because of this, a used 10D was the way to go because it let me upgrade with a little cash left over to buy some new lens and take advantage of Canon's current lens rebates on some of their most popular L series lens.
If you are looking for great entry camera into the DSLR market that won't limit your creativity, but you don't want to deal with some of the feature limitations, and build quality of the D-Reb/D-Reb XT (plastic bodies), the 10D is still the way to go. There is not a better balance of price vs. features available right now, in my humble opinion.