Have bought from: http://www.bulbconnection.com/index.cfm
Will next try: http://www.1000bulbs.com/

For "decorative" lights, try http://www.sivallighting.com/ . I bought a couple of 100' strings of C7 sockets (no plug; you can get any length you want) and twinkle bulbs for a project from them. Pretty cheap, although I was somewhat disappointed at the failure rate (5%) of their bulbs out of the box.

http://www.hsiprodsvcs.com/