Weight trainning would be great to add in at this point in you workout.
Try free weights, they are a little harder to get use to, but are way better than traditional weight machines, they will really help to strenghen your core.
Don't go over board, I would add two days a week specifcally for weight trainning, one day for upper body and one day for lower. Work on you abs both days. Don't have these days back to back!! Your body will need a little time to recover.
Squats, lunges and leg lifts are great to start with. You can always add dumbells to increase resistance.
As for your upper body I would try regular old dumbell curls, tricep extentions (google this one it's hard to explain with out a picture, but great for that little under arm jiggle!). Planks are great for your arms and shoulder and work your abs at the same time.
There are tons of ab workouts than you can find on the internet. I find that anything that you can to on a stabillity ball is great.
I hope that this helps. Good Luck and enjoy!!