I've always just used spray paint, not real picky, whatever I could get. clean the glass well, and give it a few light 'dustings', and then a couple thicker coats.
It probably isn't as scratch resistant as some specialty paint, but it's cheap, easy, and once the tank is against the wall, there isn't much to scratch it.
For that situation, DogFish's suggestion of latex would probably work pretty well. It won't be easy, but if you have a bit of time and can work from both ends of the tank, you should be able to do it.
I'm not sure brush marks are a concern for a tank with it's back to the wall - brush marks only really show on the outside surface of the paint, and the inside surface will conform to whatever it's painted on (the glass). Maybe with light showing throw on a lighter colored coating?