If the skin is only mildly loose Mederma cream thrice a day massaged into the loose skin will have some benefit after 2 to 3 months of use, as will microdermabrasion. However the only real thing that works for flabby arms if Brachioplasty (Arm tuck) with or without liposuction (may not be needed in your case as you mentioned that you are not obese). The procedure can be performed by any qualified plastic surgeon.

Mederma cream is a cream that contains allium cepa (made from onion) that has established anti wrinkling and skin firming activity. It works very well for superficial wrinkles, thinner skin of the neck can also become firmer. It won't do all that much for really loose skin, but is available without a prescription and worth a try. You can find out where to buy it here: http://www.mederma.com/ . It is also available online here: http://international.drugstore.com/products/prod.asp?pid=184312&catid=27319&aid=333181&aparam=sespider