Google Reader has truly revolutionized the “quotation” biz. Almost every time I find something in there, it provide more info (not to mention context) that isn’t available even as the few quote sites that bother with citation info.
I will confess to some pride in the amount of time I put into trying to find where these things come from. It may mean I have fewer quotes than some of the bigger sites, but they’re much better sourced than most. If I do say so myself.