WisBlawg has a short post with a link to a whitepaper comparing caselaw citators from Google Scholar, Fastcase, Casemaker, LexisNexis, WestlawNext, and Bloomberg. It also notes registration is required to access the paper. No big surprise: the big three (LN, WL, and BL) have the best cite check services.
Edit: registration is just your name, company, email, and zip code. Download options are PDF, ePub, and mobi.