H.L.
I have the skecher brand ones. I settled for them because I really wanted the original ones which are MBT (Masai Barefoot Technology) but they run about $250 a pair. I love my skecher ones. I think they do tone the core and the butt, etc. I highly recommend them. Be careful of the cheaper versions because they will have less support, cushion, etc.
I got mine at Kohl's when they were on sale for $79.99 and I had one of those 30% off coupons that you get frequently in the mail or email so they cost me $56 plus tax, totally worth it!
Whatever you do, just get out there and move!! :)