Programmergeek did an excellent job of summarizing the problems wall placement gives rise to. Nicely done.
If you can stand the width, the Snell Acoustics Type A (sadly discontinued) was made to go up against the wall, and it was among the finest loudspeakers of its day.
Several manufacturers currently make speakers specifically designed to go up against a wall and deal effective with the reflection and bass emphasis problems described by Programmergeek. I'm a dealer for one such speaker, the Gradient Evidence. Its cardioid midrange pattern minimizes interaction with the wall above 200 Hz, and the coaxial tweeter's pattern is controlled well enough to avoid the walls. The bass system can be set (via a jumper) for correct tonal balance when up against the wall.
I don't have much first-hand experience with other up-against-the-wall speakers. Allison makes some, and speakers in the Klipsch Heritage series are designed to go up against the wall (or even in the corners, ahem). Omega and Cain & Cain fullrange single-driver speakers are going to work well up against a wall also, I peddle one of these and yes I admire the other as well. I'm less familiar with Tannoy and Kef coaxials, but that format would help minimize the midrange and high frequency reflection issues; I don't know about the bass though.
At some point I might bring out a fairly high-efficiency design of my own that would work up against the wall, using well-controlled radiation patterns in the mids and highs and adjustablity in the bass region. While it's not like nobody is doing it, this is an area where I think there may be room for a bit more competition.
