So being a legendary cheapskate, I've been investigating the use of cardstock terrain pieces and "props" for my games.  The basic idea is that you print a PDF onto some medium weight cardstock, then cut/glue it together.  You can print as many copies as you like, and if you screw up, it's easy to print a new page.  They don't look quite as nice as resin or metal models, but you don't have to paint them and they're very, very cheap.

The bunkers mentioned earlier have been joined by some very nice vehicles from Ebbles' Miniatures.  I bought the utility and medium transport floaters.  What's nice about these is that they are designed for use with gaming, and for use with 28mm miniatures based on 1" circles in particular.  Which, coincidentally, seems to be the most common size and basing scheme for scifi miniatures these days.

I'm building up a pair of medium transports to use for "Grav/Mobile Infantry" transport, able to carry one squad of 10 figures in 2 vehicles.  I'll use the utility floater for the command section of the platoon, once I get a large enough force.  All of the floaters are open topped, so they're more like WWII half tracks than proper APCs, but that's ok with me and it makes it easier to put in the figures.

Ebbles also has a very cute "Serenity" like shuttle in their spaceships section that I'm eyeing as well, but that will have to wait for another day.