Get It Write
Get It Write: To Split or Not to Split Infinitives
Here's a great discussion on whether or not to split infinitives. What is an infinitive, you say? This will tell you and will instruct you on whether it is ever correct to split one.
Harvard University
Harvard Writing Center: Tips on Grammar, Punctuation and Style
Rather than lists of rules, this site provides practical advice on the use of commas, semicolons, dashes, hyphens, abbreviations, acronyms, split infinitives, "this," "that," italics, and underlining. CCSS.ELA-Literacy.CCRA.L.2