Ditto on the Squadron recommendation. Have used them consistnatly for years, and they have always delivered with good service and selection.
They also have a "droolable" catalogue that comes out annually, with good illustratons.
I havent built much for several years, but I'll tell you one thing -- the new kits out are enormously better than what I remember as a kid. You have to be careful, though, as some manufacturers have taken to using old molds (with old standards for detail, fit and historical accuracy) but putting them in brand new style boxes with new copyright dates. There isnt much protection except just knowing what kit issue is in what box.
In general, you cant go far wrong with Tamiya or Hasegawa kits. Some are older, but all have much better fit and molding than the department store style Monogram kits. The extra cost is modest, and far worth it. The best of the new issues almost fall together when you shake the box! Seams are tight and fit is right, panel lines recessed, just really nice stuff.
I also found an airbrush was well worth it. No other addition improved my builds' appearance as much as the airbrush. Badger makes some nice simple ones.
Take a look at Fine Scale Modeler magazine too -- excellent resopurce. Another great resource is Hyperscale (
http://www.hyperscale.com/) which is both an onine magazine and a BBS site.
Course, if you're experienced and just getting back into the hobby most of what I said will be pretty basic. Have fun no matter where you are at!