In terms of what to buy, I took the "what can I get for free" route, which turned out to be blue plastic.

Water can go pretty far, given pressure. If perchance you can collect on your back porch or front yard, you've got a nice grade down to your veggie garden, and should pick up some nice pressure there.

I've heard of folks using drip irrigation with them, or simply dunking their watering can to fill it up and wander around with.

They sell "mosquito donuts" for ponds and such, to reduce larvae. Natural-ish, I think. Or, a netting that floats on the surface would prevent mosquitoes from emerging into the air, and hopefully drawn th beasts.

Or give neighbors you don't like a bug-zapper and some japanese beetle bags.

I think you generally want your rain barrel to not be open to the air in a way that will attract many mosquitoes. Take a look at june's pictures here: http://greenthumbr.com/members/june/journal/2008/2/17/a_rainy_day_for_my_rain_barrel

You want an overflow valve to prevent the water from backing up the pipes after a few heavy rains. But in general, it's closed on top.

I definitely favor the closed top version. I also second bob's idea of putting it on the back porch. If you put it there you will have great water pressure.

If I could get a brand new barrel tomorrow I would actually get one thats twice as tall. I saw one I really like at the SEE Expo a couple years ago. The plastic was black, which is good blocking out light. It was tall so it can hold more water. Finally it had cedar boards wrapped around it so it actually looked nice.

I'll be excited to see what you end up getting!