One word--eBay.
Dragon's are the best detailed, but try to get the ones without those stupid DS tracks, which are usually too long and look wonky. Earlier releases have single link tracks, I believe?
Revell are a good middle-of-the-road bargain Decent detail and usually link-n-length tracks.
Trumpeter has some nice subjects, but I couldn't get their tracks to glue no matter what I tried. The detail is very good, however.
Other small and expensive kits like UM and some other brands can be nice, but they're in a price range that I just refuse to pay.
Italeri's are expensive now too, and are in many cases just re-packaged older ESCI kits. The old Esci kits can are decent enough for a beginner, but some have serious issues of accuracy like their M60 and M1 Abrams series which have one-piece wheels which look totally goofy. You have to cut grooves in between them to look like two wheels, as is proper. They have both a rubber-band track line (early molds) and an older link-length track which is much better in appearance. Hasegawa kits are on the par with these.
Stay away from Airfix. Pure amateur stuff.
You might also be tempted by 1/76 scale. Not too much in this caegory, but the old Nitto kits can be downright impressive in that scale; some of them actualy contain rudimentary interiors.