One great resource I use everytime I get a restriction requirement is this article by Brian I. Marcus, “Amendment and Response in the Mechanical Arts [pdf]” PLI Advanced Claim Drafting & Amendment Writing Patent Prosecution Workshop, Practicing Law Institute (2002, 2003).

[Update:  Fixed broken URL.]

Related posts:

1. Article: Creative Claim Drafting
2. University of Rochester v. G.D. Searle & Co., Inc., et al. (Federal Circuit)