Another vote to make sure it's both CV and CC capable (constant voltage & constant current respectively).
The above recommendations are the way to go (I'd add Tektronix's CPS250 to that list). Currently however, there's a number of
GW Instek GPC-3020 PSUs around for decent prices (it's a triple output model and has CV & CC modes). The one linked is less than $100 shipped.
FWIW, dual, triple, or quad output models tend to be a much better bargain IME than buying a lot of single output units.
As per voltage, if you'll be working on op-amps, you'll want more than 15V. ~30 - 32V models are usually the norm manufacturers produce as they're quite versatile.
Good luck.