The most commonly used Drop-vessels used in the Imperium are the massive 'Colossus' troop carriers, used by the Imperial Guard and Adeptus Mechanicus, which possess the capacity to carry full companies of Imperial Guardsmen and thier support vehicles, directly into the heat of battle. In addition to these are numerous Shuttles and secondary landing craft - some, dedicated assault craft, like the 'Shark' assault boat found attached to Emperor-class battleships, and thier Dreadclaw equivalents, as used by Traitor forces, and the Thunderhawk gunships used by the Adeptus Astartes and the Inquisition.
After that, there are the other Notables: Drop Pods - more accurately known as BEVs (Ballistic Entry Vehicles), the Astartes-pattern Drop Pods, as well as the 'Deathwind' and 'Purgatum' variants, are designed simply to deploy troops at high speed to the surface from orbit - the average time required being not more than 15 minutes, from launch to landing. Beyond that, there is the Drop Ship - a colossal BEV, easily the mass of a Reaver-class Battle Titan, containing the capacity for roughly 80 soldiers of up to Space Marine size, as well as up to 6 Armoured vehicles of Rhino-size, or 4 of Land Raider-size, plus any warriors contained within those vehicles.
Hope that helped - The standard Imperial landing craft, as detailed in the (currently in playtesting) Epic: Armageddon rules. There are no doubt lots more, but those are the combat ones that I know of.
[/b]