Any of the wierd Russian stuff, try to stay away from. PST has a few nice tanks, the KV-1 and 2, aren't too bad. The old Matchbox kits are something to be desired. And Arii's armor should be avoided like the plague.
But, the good stuff is Revell/Germany. Their kits are fantastic, about $12. (only thing to look out for is they have some kits that come with soldiers, if the armor kit in the set is not in the regular "kit only" lineup, stay away, it's a Matchbox kit!) The real winner is Italeri, they have been reissuing the old ESCI kits, and they're all under $10.
Hasegawa kits are good (just like their airplanes) Fujimi's are good as well, but they are in 1/76 scale. (If you see a kit by Nitto, it's a Fujimi)
ESCI made some of the best 1/72 armor, luckily Italeri is bringing it back a little at a time. You can find the old stuff on eBay, but expect to pay top dollar, 1/72 armor is coming back with a vengence.
Hope this helps you out,
Bernie the K.
St. Paul, MN