One thing you didn't mention is size? Will the entertainment unit be built with the speakers in mind and around them? If so, there are some minor things which can greatly help the sound. As for the speakers, there are speakers which will work in a "built in" type application.
Triad would be one I would put at the top of your list, but I'm not terribly familiar with their lineup, but I believe the Platinum LCR are some of the best they offer. Maybe Paul of Triad can jump in on this one.
For a few more good options I wouldn't hesitate with the NHT VS-2.4, and VS-3. These are designed to be placed against a wall, and will work well in this type of situtation. The other definite speaker to consider is the Aerial LR-3 and CC-3. The only problem with these is that they are somewhat in-efficient, but as long as you aren't sitting 30' from the speakers, and you have the speaker set to "small" with a decent sub in the corner, these will still sound better than most any other speaker in this situation, and would be similar, but different (depending a lot on the model) than the Triads I suggested above.