Space marine armies are so lucky. They have one vehicle chassis for most of their vehicles. Only the land raider is different for the tanks
If you really look... the Eldar and Tau do as well... Most armies, barring the Necrons (with only their Monolith) and the Tyranids, have a single chassis design that most of their vehicular options stem from, and then will have an alternate or two to keep the race's motorpool from getting boring...
Marines have the Rhino, but then they also have the Land Raider, Dreadnought, and Land Speeders (also Chaos has the Defiler and Sisters the Penitent Engine)
Guardsmen have the ubiquitous Russ and Chimera chassis, as well as the Sentinel
Eldar have the Serpent chassis, backed up by War Walkers and Vypers
Tau have the Devilfish chassis, backed up by Piranhas and the various Suits
Orks have whatever their sinister Meks will create for them for use as Trucks, as well as looted vehicles, Kans and Dreads, Buggies and Koptas
Dark Eldar are actually more 'thin' on options than any other, as they have only 2 vehicles based on the Raider chassis, and no other vehicular options at all. Though, I doubt this will remain so for much longer.
It seems to me that the only armies that do NOT have a nice selection of vehicles (apart from the prementioned 'forgotten' Dark Eldar) are those armies whose themes would prevent their use. The Nids and Necrons really would look silly in a Jeep, and those armies have no need for main battle tanks or transports.