I do a lot of shopping at the 99 Cent Store & Dollar Tree, because they're cheap and easily accessible by bike And CVS too, because of their Extra Bucks promos like CGW said.

But as for where I really like shopping: Amoeba (regional record store here in California... or any record store, really!), thrift shops, book stores, Hot Topic (sometimes they have gems!), comic shops... those are all places I end up spending a lot of unnecessary money, haha