Bumping this for you because I'm interested in this too! Ds2 is still bf and I'm a sahm and going to a gym plus putting him in a creche just seems too much hassle. (I did try it when he was about 5m old but he didn't settle very well and it didn't leave me much time to actually exercise.)
Dp and I have an exercise bike which has been a good buy, it's not just used as a clothes hanger. I probably go on it 2 or 3 times a week, and try to do Pilates once a week too (on DVD) but that often gets pushed out by other urgent things (like looking after poorly kids or sleeping). If I were choosing I would probably have bought a cross-trainer instead of a bike though, to work the arms as well as the legs.
But the boys got a Wii recently and even Wii sports is quite fun, you can work up a sweat doing the boxing! Wii sports comes with the console. I don't know how much it costs if you buy the Wii Fit and other bits. But get some rechargable AA batteries and a charger for the controllers, as the batteries go down pretty quickly imo.
I got Wii fit at christmas to get fit before next pregnancy, DD is 2 and we were thinking of making a sibling. Got pregnant. Got SPD. It's gathering dust until 6 weeks after the birth! I really enjoyed the bit of use I did get. It's so much easier than going out to a gym if you have a DP that works late or if you're a single parent.