well, first things first; get yourself a guard codex!
if you can still get your mits on some of those apocalypse deals, then i'd say go for perhaps the russ squadron set, or if you can aford it, the emperor's (re: warmaster's!) fist tank company. 10 russes for only $350(can) as compared to $550 if you buy 'em all individually... that's basically most of an armoured company right there!
failing that, get a cadian or catachan battleforce and perhaps some chaos spawn to add a bunch of mutatios to your traitors...
cheers!