I've got to back Ben up on the DOS MOS, great sound with the buffer (the battery ran out and the sound suddenly sucked!).
As another alternative, look at using a Rangemaster boost (so many guys from the 60's used them, it is probably easier to say who didn't!).
I also like the Boss Blues Driver and the Blackstone Overdrive, but these are not clean powerboosters, but will make your guitar cut through. Having heard the Duncan Pickup Booster, all I can say is 'not impressed'.
Another option is the Burford Solo/Master pedal
http://www.projectguitarparts.co.uk/Pages/electronics.htm. This works in a totally different way to the others. It is passive and you set your lead sound first, then swich this in for your clean sound. Having used a lot of Alan's stuff, i can tell you it is all really quiet and does what it says. So if your lead tone on the amp is good, this might be the best option.