I was having a conversation last week and I said I was “wracking (racking?) my brain”. When used in verbal form, it doesn’t matter how you spell it, but there are two different words, and as a writer I like to use the right one. So I went to Dictionary.com for more information.
Apparently, “to rack”, in this context, means “to torture” or “to torment”, whereas “to wrack” means “to destroy”. So really either one works, although they say “racking” is the more commonly-used one, so that’s the one I’m going to stick to when I’m writing.

The context was that I was racking my brain to think of new ideas for blog posts, especially since I’m going to be in Austria for two weeks later this month and it isn’t for any kinky or sexy reason. (My new job is sending me there for training.) So I have to rack up (yet another version of “rack”) enough posts to last until at least February 7, because I’m sure when I get back the last thing I’m going to want to do is sit down and write. The flight home is nine hours, and then I’ll have to go through immigration, and then it’s an hour home from the airport. I’ll be lucky to make it back by midnight.