Lee Valley for their stainless steel shovels and pruning tools (including a fabulous pruning blade for my reciprocating saw).
A. M. Leonard's for just about anything -- good prices, too, IMO.
Gardener's Supply seems a little $$ to me, but they have very good quality items, including beautiful, sturdy planters.
Collections Etc for garden decor, from gnomes to wind spinners to bird feeders. Their resin ornaments, in particular, are well-made (although I do always put a coat of clear poly on anything like that to help preserve colors). I've gotten a few lemons (hummingbird solar lights that never lit), but mostly a lot of bang for your buck. Also, my MIL loves their pretty tops!
