Most of them are compatible with the VESA standard.
There are three sizes of VESA mount, C,D, and E, depending on the size of the TV. Most regular LCD's use the 'C' size, large plasmas use the 'E' size.
Quite a good explanation [broken link removed]
You'll get the regular mounts in Power City and the like, eBay may be a bit cheaper. The Rolls Royce mounts are by Vogels,some of which can rotate vertically to level the screen, which is handy because it can be quite awkward to get a bracket level.
You need good solid fixings on the wall, preferably some type of rawlbolt.