These are small, low-noise, low drop out, voltage regulators. Perfect for simple applications, they require only a 4.7uF output capacitor (for stability) and have a 7V maximum input (10V in the datasheet?). Cheap and small, we use them in many applications in unison with the 10uF Tantalum Capacitor.
These little guys output a max of 150mA which is fairly impressive for such a small footprint. They have an enable pin that can allow for power saving, but the quiescent current is only 85uA so we usually just pull the enable pin high.
SFE Footprint Library
FP Name: SOT-23
TI part # : TPS76350DBVT (5V Output)
Digikey part # : 296-2707-1-ND (5V)
Single Piece Price : $0.84