Hey all,
Since I just moved back to Austin, I haven't been doing much lately. However, once in awhile, when I'm low on funds, and am looking for something to do, I look up free events on austin360.com, or do512.com. 
Now, maybe you might not be in Austin, so try searching 'free museum days', 'free things to do (enter city here)', or even 'free events in (city)'.
You can find so much to do that way. I've been to museums, movies, and Broadway shows, all for free! And if you live in a larger city, you can find A LOT of events. So go out and explore the great world around you.

Happy hunting! :)