Nikke's 2011 "Abstract RTS Model Pack," converted to .blend files.  Unzip and import the AbstractRTSModelPack folder into Unity for instant prefabs with sane defaults.

Contents:

• 3 Aircraft
• 3 Tanks
• 3 Anti-aircraft tanks
• 3 Turrets
• 3 Anti-aircraft turrets
• a Robot
• a Factory
• an Airfield
• 3 Build blocks
• a ground plane with grid; sized to fit the above meshes 

Some models offer variants that can be used in your games as upgrades / more powerful units.

Please link to Ironbane (www.ironbane.com) when using these. Thanks! Oh, and should you actually make a cool game with it please let Nikke know ;)

The original pack from Nikke can be found here: http://opengameart.org/content/abstract-rts-model-pack