I'm going to build what I'm pretty sure is the biggest Joule Thief, if not the biggest blocking oscillator alone, on the internet. Which is pretty sad when you think about it. But in any case, what I had in mind was...
In simulation (here at school, I happen to have access to a simulator but not a Bench...I'm so ashamed), this circuit runs around 5A peak collector current. I have the inductance set to 400nH and it runs around 500kHz. Input is a couple of watts. Efficiency is around 70%, which is quite good for silicon at this voltage.
I haven't decided if I want rectified and filtered output or if I'll drive the LEDs directly. They may be more efficient with direct current, justifying the 0.3V drop of the diode. The ten LEDs will probably share current well enough...we'll see.
I remember Watt Sun whining that there are (almost?) no good transistors that run low Vce(sat) and high Ice. The 2SC5001 is under a buck from Mouser, so for the scale this sucker is built at, that's not too bad. For medium stuff, you can't beat Zetex parts, but they're still expensive, even for one offs, and especially compared to something like a 2N4401, which I think works just fine in a regular (one or two LED) inverter.
Tim