The Independence War Paper Models site has some very nice — and free — paper models of starships.
Interformic Games offers a free miniatures game called Turn or Burn. The authors write:
Turn or Burn is a fast-paced game of space fighter combat for 2 to 8 players. To start a game, you design your fighter from a deck of system cards. Each turn you play a system or maneuver card facedown to plot the action your fighter will take. The game uses vector movement, so you must plan ahead! When everyone has plotted, all players reveal their actions simultaneously. Fighters move, guns fire, stuff explodes, and it’s on to the next turn.
There also are several modules for more detail.
Here’s a treasure trove for you science fiction miniatures wargamers: The Starship Schematics Database has illustrations of hundreds of spaceships form the Star Trek, Babylon Five, Space Battleship Yamato and Battlestar Galactica universes. I think these would particularly useful as a source of illustrations for home made counters for your games.
How big is a Stardestroyer compared to a Romulan D’deridex? Which is bigger, a Vorlon cruiser, or Farscape’s Moya? This great site has size comparisons of the great ships from science fiction.
The Heavy Metal Wargaming site has some counters for use in starship games set in the Star Trek: The Next Generation universe.