I have not been looking into AV receivers lately, but you need to decide on features and connections (i.e how you are going to link up to your TV / flat panel / projector and at what resolutions; how many speakers are you going to have, etc). Many now offer upscaling of video signals.
I used to own a low-end Denon and am currently using a Pioneer VSX-D2011. And I basically agree with ex0du5 : Denons generally sound warmer, Pioneer amps deliver more resolution and sound brighter. Yamaha does good cinema effects, meaning good surround sound processing and loud effects; generally supposed to have less finesse with music at the budget end of things (obviously depending on model too). Also the new Sony's with digital amplifiers have gotten some very good reviews too, but have never heard or given them trials, so this is "hearsay".
One of the pros about the Pioneer I have is it has 7 speaker channels, but 2 can be re-routed for use for the front pair - basically bi-amping them. It was one of the first "affordable" AV receivers to offer this, and I assume more models have this feature now. Most non-entry level AV receivers come up set-up mics these days, or at least the Denon's, Sony's, Yamaha's and Pioneers do anyway; if I am not mistaken the mic setup feature was pioneered by Pioneer. Anyway, I am happy with the Pioneer and see no need to upgrade in the near future.