As someone who has not built a gundam model before, is this any good? http://plamoya.com/en/tengen-kadou-gurren-lagann-full-drillize-ver-plastic-model-p-52835.html
Haven't seen that one before, but it's by Kotobukiya so you can't go wrong.
Bandai is the king of model kits, and Kotobukiya is a strong runner-up. The only others Koto kits I've built were the Rockman ones, though I've got my eyes set on the EVAs.
That said, the best places to get Gunpla from, besides your local hobby shop, are AmiAmi or HLJ if you're importing, or else Gundam Planet or, if directly by Bluefin, Amazon. Keep in mind that the boxes are HUGE, so shipping will add up. It's best to get a few kits at once than one at a time.