Your doc will be able to advise you. No skydiving, bungee jumping etc, anything where there's a risk of a big fall. Skiing is also out. I still cycle though, and everyone's pretty happy with that.
Don't do anything you weren't doing before you were pg, unless you check with your Doc.
Your heart rate is best kept under 160bpm (my doc said that I'd know if I was going too hard, and it's true - I have never set off the alarm on mine, I feel it first) some say 140bpm, but my doc is happy with 160.

And, fromt he look of the second hand book I got on the subject, you should have a bad 90s haircut with a leotard worn over leggings for all exercise