I'm months behind on my magazines as usual, but read Randy Mosher's article "Spicing Up Your Beer" from Mar/Apr Zymurgy last night. He referenced a few online spice sources, but I want to list some others too.
World Spice Merchants - awesome selection and great info on spices
Taste Pad Thai - great source for fresh Thai spices (lime leaves,lemongrass, galangal, etc)
I haven't tried Randy's sources, but want to include them so later when I'm looking for something I can just come here instead of trying to find the right magazine again. The search button for my house is usually broken
Gernot Katzer's Spice Pages - Nothing for sale, good info
Wild Weeds - Botanical supplier, they have Myrica gale
Monteagle Herb Farm - Another botanical supplier
San Francisco Herb Company - Large culinary herb supplier
The Spice House - Culinary herbs and spices including bitter orange and grains of paradise. Retail outlets in many cities
Penzeys - Culinary herbs and spices, retail outlets in many cities