Milt:
You can actually mix LED with incandescent bulbs since the incandescent can run off of AC or DC. 12V bulbs would match up just fine with any LED strip you want to run.
For bulb and socket combo I use Model Power 511 (12-16V) - Walthers
For make my own (door lamps / hanging lamps) I use grain of wheat bulbs from Miniatronics 18-028-20 (14V) or 18-016.20 (16V) - Walthers. I was also turned on to Cir-Kit Concepts Inc 12V bulbs with 18 inch leads by alan Graziano - again Walthers.
The last time I bought LED strips I did so from All-Electronics. It was a reasonable price for a roll of 500.
Joe
PS - if you want to spend the money Woodland Scenics just came out with a ?Plug and Light? lighting system a lot of people are raving about.