I usually order from MV.
I've also ordered electronics stuff from Digikey and/or Mouser if you wish to check them out. Although there isn't much about e-cigs that is actually e-cig specific (read connectors mostly), MV has sorted out a lot of this and is a good supporter of the community. Thus, I choose to support them. However, general electronics parts can be had at a lot of places. RadioShack included.
Kits, on the other hand, are e-cig specific bundles of stuff and MV is the only one that I can think of at the moment.