[2porscheguy]

"Saggy" arms are usually due to under-developed triceps much more so than your biceps, as your triceps are quite a bit larger than your biceps (^^^see kach22i's excellent anatomical pic above).

You can still accomplish quite a bit even with just dumbbells in terms of working out your arms. You'll need a good sturdy adjustable incline bench though. Here's what I recommend for exercises:

Biceps: Seated arm curls (these are easier on your lower back than standing curls) and concentration curls

Triceps: Horizontal triceps extensions (lie down on your back on the bench and using light dumbbells extend your arms) and bent over triceps extensions

You should do these no more than twice a week to allow for recovery of the muscles involved.

I would however recommend that you follow a more extensive work out program to target both upper and lower body and not just working on your arms..my $0.02!