I have a few nice Taylor Schrades that I really like. The 105 and 106 models are actually quite well made and very inexpensive. The steel takes a razor edge. Also, Kershaw makes some nice inexpensive models that fit your bill.
Sorry, the Schrades I mentioned above are dual thumb studs, not flippers - I would still recommend them. Do definitely take a look at the Ontario Rat II - great knife.
Rich
Just thought I'd chime in to point out that the SCH105 and 106 have been discontinued.

If OP does not mind < 3", SanRenMu makes quite a few nice flippers but those aren't locking folders. Instead, they use two bearings to lodge the blade in the open position.