I want to be able to see the FPS I'm running at, as it feels a bit low.
tdt in the console to no avail.
FRAPS can be used for showing your FPS, as well as recording your gameplay, but that will require you to buy the full version.
A self-described simple, bare-bones FPS counter. Does exactly what it says on the tin. I use it, I like it.
Has a couple extra features, too. There's a key to toggle it, a key to change the corner it appears in, and even a key to change the priority of the Skyrim process. Everything configurable through the INI.
It's an SKSE plugin, but apparently there's another way to use it if you don't want SKSE.