Also for unusual but not necessarily cheap stuff:
http://www.geeks.com/

For electronic stuff, good prices, often equipment pulls but many new items:
http://www.allelectronics.com/
Get on their mailing list for a free catalogue.

And of course the old standard that everybody loves to hate:
http://www.tigerdirect.com/
They are often one of the first to offer something new and sometimes their prices are good.

For cell batteries:
http://www.all-battery.com/index.asp...S&Category=196

For electronic parts for older equipment (especially electronic musical equipment)
http://www.tubesandmore.com/

And one that belongs with my other list but it probably has USB warming slippers:
http://www.volumerate.com/

Enjoy and again - no connection to any of these or guarantees of sucessful purchases