Suppose you cannot use players' or DM apartments. Where would you play a whole campaign ? For the very nature of roleplaying, pubs and public libraries are not appropriate. Any proposals ?
Actually libraries and pubs are both good choices. Our local historical mini's club routinely uses the library and The Escapist sponsors Terra Libris, a project to play RPGs in libraries.
A local group plays in a 24/7 McDonalds on Friday. We have a local university sponsored club.
I've played quite a bit in coffee shops. Just keep buying refills and the occasional pastry. Hell, I suspect we spent more per hour than the local college students who were studying.
Malls and some big box stores have activity rooms. These are easier to get as a club, however.
If you have a good gaming store, they may be willing to host your gaming group, especially if you are good customers of the store. It depends on their space--but I've managed a Saturday game at a local game store for several months. This is usually a better option if your game is open to new players, but it can be useful in all cases.
Libraries and public universities often have reservable private spaces that members of the community can use.
Pubs and restaurants similarly often have "private rooms," if you are going to be spending money on food and drink and not just freeloading.
Many privately owned public spaces (malls, etc.) will tolerate you depending on your behavior, especially if you pick a place and/or time that they're not very busy.
Many game stores have some gaming space, though I consider this to be an absolute last option.
I played in a game hosted in the food court at the Dobie Mall in Austin - it's a nearly-abandoned mall near campus, so we certainly weren't disturbing anyone.
I also helped organize a local RPGA club in Memphis, where we used libraries and game stores to host game days.
Back in school, my group occasionally ran into this situation so we made use of the picnic tables at the public park when the weather cooperated. Of course we always went for the tables that had a good amount of shade to avoid all that healthy and nurturing sunlight.
Depending on your town I think you'd be surprised at what the local libraries offer that would make good space. The major problem being hours if you are looking for a game in the late evening.
My dorm had a "tower room" that overlooked most of campus, and was setup as a library that was rarely used, especially after hours. We would push the tables together and have the an excellent gaming area.
The ambiance of playing in a freaking tower was also cool.
R.K. Milholland of Something*Positive once mentioned that he and his friends used to play late-night at Denny's. They just kept ordering coffee, and the only other people there at one in the morning were truckers and sleeping goths.
Community Centres would be the first place I would look. You might need a membership, but they should be pretty cheap, and of course being a paying member entitles you to use the space.
I've adapted my attic for a gameroom and it served us well except days with temperature over 30 and below 15 grades Celsius. I totally recommend that.
If still at school you can ask for an unused cellar or attic as well.
For older people pubs with lots of small rooms could be promising :) You can set reservation on a table in a tiny room where you'd not be disturbed nor disturb other people [rpg players can be disturbing to watch :P]