One piece cranks were used by BMX long after they'd been phased out on other bikes, so most of your parts options will start there. Pedal threading is 1/2" instead of 9/16", which will reduce your options. You can get a spider to run regular chainrings. IIRC, Sunlite still sells double and triple chainwheels for one piece cranks. If you decide to go for a single chainring up front, you have a wide range of gearing options thanks to BMX, but make sure you get something with 3/32" teeth to fit the chain.
Switching to a three piece crank will save about a pound, and give you some more crank options. Truvativ makes a conversion that fits into the BB shell and lets you use a regular ISO-thread bottom bracket: Width of both OPC and English BBs is 68mm.
http://www.amazon.com/Truvativ-00-64...581502&sr=1-15