I'm using the Linear Technology's LT1937 for a project I am doing right now; for my purposes it drives two series white LEDs but it could drive more. There are various configurations, but the minimum configuration would just have the chip, an inductor, a couple caps, and the schottky diode... I think. You can also configure it with output clamping and soft start. Oh yeah, you need a current sensing resistor, too, since it is current controlled.
It seems to work fine, and is in an SOT-23-5 package.
j.