Suggestions for 20D replacement/upgrade?

Need advice on a camera upgrade from the Canon 20D. I want to be able to use my lenses, but am not sure which models to look at, as there are so many fricking variations since I got the 20D originally!

I was originally thinking about just getting a used replacement 20D, but it's 8.2 MP, and they're up to 18 now. The highend models are out of my price range, I'd like to stay under $800.00 if possible. May have to go with something used at that price though.

I want to be able to do full manual override, and would like something that's pretty decent at night photography, as I like doing a lot of that.

The Rebel T4i is about the right price, but I'm not sure how the quality would compare to the 20D. 

Open to suggestions.