Don't know your current lithium dosage or your levels, but if you can, you might want to raise it.

I've taken sodium valporate, which is good for squashing mania. It's not good for the depressive side though, so it depends on which end of the spectrum you visit more and what has greater impact. Usually you can augment sodium valporate with an AD if things start getting rough. Also I don't know the price of it in America - I believe that, state-side, it's sold under the brandname depakote [or depacone, which IIRC is the liquid version].