The United States has finally come around to supporting a No Fly Zone over Libya and in fact now wants to go further, with a no-drive-zone. Gaddafi is using his artillery and tanks far more than his (rather antiquated) air force, so this would help the rebels quite a bit more than an NFZ.
I think that an NFZ (at least) is necessary to protect the people of Libya from a massacre. If Gaddafi attacks Benghazi, possibly next week, thousands of people are going to die in the attack and in the reprisals afterwards. Gaddafi has publicly executed people in the past and would likely do so again.
There are concerns about us being sucked into a war in Libya; however, we are being asked by the rebels to help. If we allow Gaddafi to win, we will not only have failed as an international community, we will have to deal with another rogue state; because there is no way "normal" relations with Libya can now be restored. Libya could well restart its WMD and long-range missile programs. I don't want that.
I don't like the idea of entering this war, but it is the lesser of two evils.