I've had been looking for a good price/performance option for my nodes and stumbled across these on eBay. The seller I bought from (recyclepowers, item number 180623038782) supplied 4 of the 14500 cells for a very reasonable £3.54 inc delivery. These seem ideal for powering the USB JeeNodes due to the on-board Li-ion charging circuit and I have been running one like this for a few days now (battery holder stuck with a stick pad to the rear of the node and fly leads soldered to the power pads) - just though I'd share this with you :-)
NOTE: Li-ion batteries can discharge at an 'explosive' rate if shortcircuited! Some cells like the wire-ended variety have protection circuits buit-in to stop this happening, the batteries mentioned above (AFAIK) DO NOT. NEVER connect these to normal (other than the USB type) JeeNodes WHILE POWER IS BEING APPLIED VIA ANOTHER SOURCE.