Heck, that's an easy answer: Savage Worlds!

You can grab the Test Drive rules which contain a good portion of the core RPG, and that can give you a good starting place. But, for wargamming, what you really want to grab is "Showdown" (also free to download), which is the Savage Worlds skirmish rules.

I'm currently running an Iron Kingdoms (Warmachine) RPG using Savage Worlds, and playing in a pulp 1940s style space opera (think Flash Gordon), and it's definitely my system of choice. As for wargaming with the Showdown rules, a buddy of mine and I threw together a WWII game using 1/72 models (we each had around 100), and jumped into it. I've also played the couple of free wargame scenarios they have. It plays very nicely--quick, easy, but not too simple as to amount to just rolling dice.

You can get more off of the publisher's site (which also has some forums) at http://www.greatwhitegames.com