Inside:
exploring the house. We play with light switches, go to different parts of the house we don't usually play in (attic and basement), play with the pets (we have two cats, one of which really likes my son, and a dog, who also is very good with my son), and opening up cabinets/drawers.
housework. I either put my son on my back in the ergo or carry him around to vacuum, sweep, mop, do laundry, pick up...just about anything. Sometimes when I'm doing a chore he really just likes to sit and watch! Hey, it kills a few minutes and gets stuff done!
dance. My son (who is 9 mo) just recently got into dancing. He will hold himself up on something and bounce when I play upbeat music, and I dance with him! Great work out and lots of fun for both of us. If he doesn't want to dance on his own, I hold him and dance with him.
work out dvds (can you tell I'm still trying to lose the baby weight?

). I have netflix and have found a few good baby and me work out dvds that Wyatt likes. It's worth a shot.
Out of the house:
museums. Even though he's too small to walk around, he really loves seeing all the other kids playing, and we got a membership to the local museum of play for a pretty good price. It's worth looking into.
YMCA. I got financial assistance for the YMCA (I only pay about $10 a month for a full membership!) so we go there a few times a week and I leave him at child watch (which is really great here) so I can work out in the next room. It's such a nice break for me and change of scenery for him. I love it!
I hope those suggestions help a bit!