Now I can happily tell you what I have tried, but motivation is quite a different matter.
dp bought an exercise bike just after ds2 was born and I was not impressed, thought it was just another needless expensive gadget he'd allowed himself. But at the moment he's using it almost every evening after the kids are in bed, sometimes for up to an hour. It appears that he's far more motivated than me. I use it far less often, partly because I find exercise bikes quite boring. (When I do use it, I put it on the 'sport' setting so the work rate goes up and down to keep my interest up.)
I have some weights and for a few weeks recently I did strength exercises from a book called '8 minutes in the morning' by Jorge Cruise. I did it after I got up, and although it always seemed to take me longer than 8 mins, the boys thought it was quite funny so I didn't have to worry about keeping them occupied while exercising. Unfortunately after a couple of weeks they started getting bored and jumping on me or otherwise demanding attention while I was exercising, so that has stopped for now.
I also have a yoga DVD but this time it was my interest which waned!!
I bought myself a skipping rope and when we go to the park I sometimes have a go. I'm awful at skipping but it's quite fun - as long as my bladder is pretty empty!
The best thing so far is that ds1 (4yo) has a trailer bike which fixes on the back of mine. On Wednesday afternoons when ds2 (2yo) is at nursery, we go cycling together in the park. It took quite a bit of getting used to, as it feels far less stable than cycling on my own. I was also terribly unfit so often had to get off and push on the steep bits. But we both enjoy it a lot and try to go a little bit further each time. We haven't been for the past few weeks as it has been so hot - we've been swimming instead, which isn't really much exercise for me as ds2 is only just getting used to no armbands - but as soon as it cools down a bit we will start again.
Also, don't laugh, but when I'm pushing the boys on the swings, I sometimes run around the frame in between pushes! I realised that I wasn't very 'active' when I went out with them, so I try to raise my pulserate a little doing stuff like that.
What DVDs do you have, COV?
FrayedKnot, I think there was a discussion in the past couple of months where other people talked about what exercise they did at home, e.g. one mumsnetter ran up and down the stairs several times in the day. I can remember being quite impressed by the range of activities. I'll try to find the thread and post a link.
If you find out anything about motivation, please let me know too, I definitely need to get fitter but find it hard to establish good habits that will last longer than a couple of weeks.