Boston Acoustics, Niles, and Klipsch for a few names make in-walls. Some sound decent, but are not considered High-end by any means. Most Best Buys, Tweeter/HIFI Buys, Circuit City, will have some on display so you can listen. Most of your better AV dealers will as well and may have some much better sounding models. Once you lose control of the cabinet dimensions and design it is hard to make a high quality sounding product. They can sound good. It is your money and you get to decide. Good Luck. Some even make in-wall sub woofers.

Thiel has made an attempt at retaining control of the cabinet with in-wall speakers: http://thielaudio.com/THIEL_Site05/Pages/models/Model_Intro/modelintro.html

I should have also mentioned the Elac Imago's that are picture speakers that come with frames and fine art of your choice. http://www.q-usa.com/ is the Elac Importer and from there you can go to Elac web site and check out the models. With a decent sub they are very nice sounding and most people have a hard time trying to figure out where that very good sound is coming from. If you go to the quick-link block on the Elac website and scroll down to DML LS: Imago you can see the product and view all the available artwork. I had a dealer in Huntsville, AL who had a number of highend clients from the Space Center who bought them and were quite pleased with the results. They did use a sub. Once you get to the picture art you can click on the British flag and view in English. Some of the available art is nudes so be careful of the company you view this with. You have been warned. If interested Brian at Q-USA, the importer, can help you find a dealer.

http://www.poster-shop.com/?PHPSESSID=1487681bc6ee2a0a089d6229f496ea1d

Check out the Induction Dynamics web site.

If you intend on installing the speakers yourself, pay attention to the recommended enclosure dimensions and be prepared to put in a couple of 2x4s (2x6 if your walls use this dimension) between the studs to take full advantage of the manufacturer's design. Pick up a tube of Liquid Nails at Home Depot and predrive your starter nails or screws to make installation much easier.

While you are at it, at the very least, use decent install cable such as Audioquest Type 4. You really need to take advantage of every opportunity to get good sound out of inwall speakers.