Here is my policy, in brief, on graduate school references, because every year, I get a ton of requests for them - sometimes twenty or more, in the past. Even though they are largely webforms now, they still take time to prepare. Here are my policies:

• For any given student, in any given academic year, I will provide a maximum of 3 (three) references. I will track which ones I provide; once three have been provided, no more will be provided, regardless of how important you think they might be. ADVICE: choose wisely what schools you will ask me to provide references for.
• My references are based SOLELY upon what I know of your academic and/or research work. It has nothing to do with whether I like you or not . . . I like pretty much everybody, but I cannot say you'd be a great graduate researcher if the only thing I have seen of your work is intro CompSci and Digital Systems. You should be focussing on your third and fourth year instructors for the best references.
• References will be provided in sealed envelopes, with a seal-signature on back, and sent directly to the institution (unless there is a specific directive from them to the contrary, but if there was, I'd question their methodology!) I will also provide references via private electronic means. Public or open-envelope references are not provided.

Note: if I have previously caught you in an act of academic dishonesty (a violation of academic integrity), I will not provide a reference for you for any reason whatsoever. I cannot recommend anyone who cheats to gain an undeserved position.