Can anyone recommend any hostels near London's Gatwick Airport that are easy to get to by public transportation?

I can't help with near Gatwick, but last fall I stayed at the Astor hostels' Victoria location, about a ten-minute walk to Victoria Station. We flew out of Gatwick pretty early (took the 5:30 Gatwick Express) and thought it was a pretty convenient location, so I thought that might help if your reason for wanting to stay by Gatwick is an earlyish flight. (I have since seen recommendations to take the Southern trains instead of the Gatwick Express, since it's cheaper, so I'd check those timetables as well.) The hostel web site is astorhostels.com.

Is there a particular reason you want a hostel? I've not heard of any near LGW - but other options (priceline, B&Bs) could be almost as cheap as a hostel.

There are many hostels in London itself - and the commute to LGW is easy. How long is your layover?

there are some cheap B&Bs that are a short walk from Gatwick terminals - yes a walk - about 25 pounds a night and accessible by footpath - about a 15 minute walk. consult Gatwick airport site for details.

Thanks everyone for your help. For my departing flight from Gatwick back to the States, I'll be coming into the London area from Devon. My flight out of Gatwick leaves at 2 p.m. on a Sunday but the earliest train from Devon still arrives without enough leeway time to check in at Gatwick, so I figure I should get to the Gatwick area the night before and stay somewhere nearby that doesn't require too much wandering around to find. I wouldn't mind staying elsewhere around London as long as it's easy to get from the place to Gatwick Airport. I appreciate your advice!

W/ a 2 p.m. flight there really is no reason you have to stay near the airport. What is your budget?

Have you been to Brighton?

Just a thought, Gatwick is half way between London and Brighton. You can get any budget accommodation including hostels in Brighton.

It's a nice place to wander and chill for a day or half day before a flight and then you can get a train directly to Gatwick in the morning.

As you'll be coming into London from Devon, the best place to stay is London. With a 2:00pm flight you have the choice of virtually any hostel in Central London

Some nice B&Bs in the little town of Horley, about 5 minutes from Gatwick. Also a good pub in that town. Most of the B&B owners will pick you up and return you to the airport at no extra charge. We stayed in several but this one is our favorite:
http://www.gable-end.com/index.shtml
They get great reviews on Trip Advisor.

We also stayed at a B&B in Horley. Very basic accommodation. On the main road, so lots of traffic noise even at night. Comfortable and sufficient for our needs. There was a very nice restaurant/pub in Horley. The manager drove us back and forth to the airport.

Budget?

Horley is actually a short walk from Gatwick terminals - i often walk to it after i check in early for my flight

there is a footpath that in about a mile comes out into the town itself.

there is actually a B&B right where the footpath comes out - about a 20 min walk from terminals. I've seen airline employees coming out of it and walking to the airport. On a very quiet street - don't know name but something like Granny's B&B.

the OP is coming from Devon. S/he wants to use public transport Getting to London will be easier than to LGW. Plus there's a much larger slection of hostels if that is what he wants.