I've heard a pair of Polk in-walls that suprised me by how good they actually sounded. The image they provided was more solid than some bookshelf speakers I've heard.
M&K also makes in-walls. Knowing the quality and care they put into their speakers, they're probably worth checking out if you have the funds.
Remember that with in-walls, you still have to set them up almost like regular speakers to get the best performance. In other words, they should be spaced evenly along the wall and at about the same height. Also, like all construction projects, make sure you measure twice!