I'm giving up "free time"--and devoting it instead to more prayer and charitable works. I've realized that having my free time is something that I cling to heavily, so giving it up will be a challenge.
Remember, for those participating in Lent, the aim is to give up something *good* because through deprivation, we are reminded of our mortality and our need for the Lord, as well as train our focus on matters of the spirit.