BMA's great but their website prices aren't the GREATEST, I mean they're cheaper than anything here but if you know him personally he'll give you a much better price.
Tomek's tried this place and they seem for real, their prices are as good as BMA and better in some cases:
Locally, for new parts go to Bruno @ Racing King (racingking.net, or PM Bruno on this site). The best guy and great price for a Canadian dealer (US is better if you smuggle it across the border, otherwise Bruno will be even better). Will Z of WillZ.us (firstname.lastname@example.org) will get you wicked used parts for great prices (got my 95 M3 rack from him), a friend of mine, one of the best, he's instructed me at Mt Tremblant.
If you're in a huge rush for an old rusted piece of crap part that will let you pass safety, then you can go to Shantaram (BMW Used Parts on Steeles). He's a good guy but he makes money off the suckers and he knows that. Some days you come in and he'll quote you a price higher than a new price from the dealer. 2 days later you ask for the same part and it's half the price. I keep coming back until I hear what I like...