One of my favorite topics!
You should check out the HTD (Home Theater Direct) line, especially their high definition models. I haven't tried these myself, but am thinking about ordering a pair of the HTD-AL W80 for $160 per pair.
http://store.yahoo.com/htd/highdefinition.html
The HTD brand is not well known, but the performance to value ratio is supposedly incredible because it's an internet direct marketing firm. They offer a 30 day trial period, and since the cutout dimensions for their in-walls are pretty standard, you should be OK in case you need to return them.
I've used a pair of Polk Audio AB755 which are available for around $200 per pair (discontinued). These are fairly decent, but the AB855's are a step up if you can find any these days.
The older Niles Audio in-walls are also a great value. You can find the Niles HD800 for around $300 per pair now that Niles is pushing it's AT series at much hight price points. I like the HD800 a lot!
The BIC VI-38 goes for about $150 per pair and has received great reviews. I've not tried them myself, but they are worth checking into.
On the high end, the best of the best IMO are the B&W Signature 7 series (there have been a couple of different versions). These pups are full range and simply amazing!
You can't believe these are in-walls. Astonishingly good and worth the $1,200 per pair that they fetch. I'd love to know if anyone has compared the B&W Sig 7's to the Niles Audio AT8700 (top of line). If you are thinking about buying multiple pairs of anything in the $200-$300 range, IMO you would do better with one pair of Sig 7's for an awesome 2-channel experience.