Letters of Recommendation

I'm looking for some advice on how to ask for letters of recommendation. The "catch" is that I graduated in May of last year and most of the professors that I knew fairly well I haven't seen in almost 2 to 3 years. How should I go about asking these professors for a letter of recommendation? Should I e-mail them first to explain my situation or should I just wait outside their office to catch them? Will it be a problem that there is a good chance they most likely won't remember me and how...

Letters of Recommendation