The Internet Grammar of English is a great site for brushing up on the mechanics of English. In my Greek and Hebrew courses we spend a lot of time teaching the fundamentals of English before we can move on to the foreign language. Save yourself some time and read through the Internet Grammar of English before you get too far into your Greek or Hebrew course. Or, read through the Internet Grammar before you get too far into your English courses. Or, read it before you have to write your first paper... You know what, just do yourself a favor and read through The Internet Grammar of English. You (and your professor) will thank you for it. 

The Writing Centre at the University of Ottowa posted their "HyperGrammar" grammar course here. The site is under construction, but already contains a great deal of excellent information and resources. The "catch phrases" section is particularly amusing for those who have to get to grade student papers.