It kinda depends on where you are starting from. Are you in pretty good shape now?
For me, a combo of aerobic exercise to burn fat and weight lifting to build muscle has done the trick. I can't say enough about strength training for women, especially as we get older.
You might also check out the exercise forums. Lots of good advise and conversation going on over there.
2.5 years, 45 pounds later... 128ish pounds