Hey I can make a recommendation. I like both the Phillips 5761 and Osram 64275. There's also a 20 volt Hikari bulb that's not quite as bright but they're only a buck and change.
www.Replacementlightbulbs.com is where I got all of these bulbs.
This is what I ordered and the prices I paid for them (plus shipping):
2x Philips 5761 6V 30W
Item # Philips 5761 6V 30W $11.70 USD
1x Osram 64250 ESB 6V 20W Lamp
Item # Osram 64250 ESB 6V 20W Lamp $2.95 USD
2x Osram 64275 6V 35W Lamp
Item # Osram 64275 6V 35W Lamp $10.06 USD
3x Hikari 6V 20W G4 ESB Lamp
Item # Hikari 6V 20W G4 ESB Lamp $3.90 USD
At any rate, if you go bi-pin, you have a ton of options. KIU's bipin sockets are great! Plus they remove a lot of resistance, although cammed reflectors don't work the same way with them I can highly recommend them, especially since you have no reason not to go with one of Litho's excellent $20 reflectors that way.