For students looking for a quick grammar fix, I recommend Mignon Fogarty's weekly podcast "Grammar Girl". This podcast (with transcripts posted on the web, for those of you who prefer reading to listening) focuses on grammar and style issues, commonly confused words, and other tips to improve your writing.Calling the show "Grammar Girl" is a bit misleading, though. This podcast is about "writing", not just grammar. That means that, while there are plenty of useful tips to be found, there are also a lot of subjective style judgments, and sometimes these opinions are mixed together with grammar rules without much thought.
My recommendation? Listen to the podcast; it is a good one! But if you encounter any rule or advice that sounds particularly arbitrary, look into it: ask your GMAT instructor, or do some digging around on the web or in a good grammar book. The podcast is right far more often than it's wrong, but sometimes it's just a little too judgmental of nonstandard structures and styles for my tastes. I've noticed that the episodes written by Mignon herself tend to be a little more GMAT-relevant; Bonnie Trenga's guest episodes delve into subjective issues of style and problems with ambiguous solutions quite a bit more often.
I hope I haven't scared you off with all of these caveats! Honestly, you're not going to get bad advice from Ms. Fogarty, so don't be afraid to dive in and see if you like it. She's easygoing and keeps the issues simple, so if you've been bored with or lost by other grammar references, this is a great starting point. I've provided both a link to Grammar Girl's main page (and iTunes subscription link) and a link directly to her "grammar" archive (the episodes I find to be most useful for the GMAT student).
Main page: http://grammar.
Grammar archive: http://grammar.quickanddirtytips.com/Tags/Grammar/page/1/sortbyalpha/
