I buy manga @ two places. The first one is a bookstore in the city where I live. They don't got much, and is slightly more expensive than option 2. But I buy from there if possible, just because I want to support them. Option 2 is
http://www.sfbok.se , a Swedish sci-fi store that sells alot of manga and anime. They import both from the US and UK, so they have plenty of stuff on English(which I prefer over Swedish). They're cheap and have an awesome customer support. The only backdraw is that it takes quite a while before my order shows up in my mailbox. Mostly between 5-10 days. If you wait for something good, then you always wait too long....