The Star Swarm benchmark uses Oxide Games' Nitrous engine to render a glorious multi-thousand-ship battle in space that will bring your PC to its knees.
The Nitrous engine put on display by Oxide Games and Stardock last month is noteworthy for its ability to render and control multiple thousands of on-screen units simultaneously, enabling the creation of battle scenes on a scale never before seen. Of course, that sort of thing requires a certain amount of processing power to get done, and thanks to the recently-released Star Swarm stress test/benchmark, you may now quickly and easily determine that you don't have it.
To be clear about it, this isn't a game, it's a demo that sets two huge, AI-controlled space fleets against one another in a real-time battle. It requires a DirectX 11-compatible video card and will also support AMD's Mantle when it becomes available, and offers multiple scenarios and visual settings from "low" to "extreme."
Because it's not a "deterministic simulation," which is to say that everything is being computed in real-time, the results of each benchmark will vary somewhat from run to run, but it's enough to give you a good idea of how close to (or far from) the bleeding edge you are. My own aging-but-still-viable rig, a Core 2 Quad backed by a GTX570, pulled down an average of 41.1 FPS at low settings but managed only 15.99 at extreme and several times bogged down to lowly, lonely 1 FPS. That's not a true mark, since I haven't rebooted in days and had a bunch of stuff running in the background, but the environment was equivalent and it was a fun show to watch, and that's good enough for me.
If you want to give it a rip yourself, you can grab the free Star Swarm stress test from Steam. Post your results in the forums and see where you stand!