Dimmable PAR38. MR16 base LEDs are now also available, run straight off 12VDC, no soldering, just need the MR15 sockets.
http://www.ebay.ca/itm/110646443892?...84.m1423.l2649
MR16 in cool white, I'm sure if you search, other colours are available, including blues. If one burns out, pull it & plug in another.
http://www.ebay.ca/itm/260807325869?...84.m1439.l2649
MR16 sockets
http://www.ebay.ca/itm/360261138385?...84.m1439.l2649