I thought I'd start a list of all the currently available rail covers. Feel free to add any that I missed! (pictures are required)
Magpul XT
Magpul XTM
Magpul Ladder Rails (also available from many other manufacturers)
Surefire Ladder Rail Covers (slight variation)
TangoDown Rail Panels
TangoDown SCAR Panels
BravoCompany 11 Rib Panels (who actually makes these? ProMag?)
Knights Armament Ribbed Panels
Troy BattleRail Covers
Ergo Standard Covers
Ergo Diamond Plate Covers
ErgoGrid Rail Covers
Ergo Redi-Cover
ErgoLok covers
Ergo RibLock Rail Covers
Command Arms covers
Mako Thermal Rail Covers
UTG Rubber Covers
Magpul XT
Magpul XTM
Magpul Ladder Rails (also available from many other manufacturers)
Surefire Ladder Rail Covers (slight variation)
TangoDown Rail Panels
TangoDown SCAR Panels
BravoCompany 11 Rib Panels (who actually makes these? ProMag?)
Knights Armament Ribbed Panels
Troy BattleRail Covers
Ergo Standard Covers
Ergo Diamond Plate Covers
ErgoGrid Rail Covers
Ergo Redi-Cover
ErgoLok covers
Ergo RibLock Rail Covers
Command Arms covers
Mako Thermal Rail Covers
UTG Rubber Covers