Free games! I have said it here before, and I will say it again. The original version of Werewolf, where you write letters (and an eyeball or two) on scraps of paper. This scales well, add another werewolf every 7 people, another seer every 10. 5-to-25 people in general, I believe, but it works great at 7-to-12.
Monikers, I have to vehemently agree with the previous posts, is fantastic for a party game. Yes, it’s not free, but it’s about 10000 times better than charades. It’s also best to not completely tell the players the rules until that round is up. And being imaginative for the “bonus rounds” is the best (“Under a blanket” “Behind your chair” and “Sock puppets” for instance). I believe this scales up to 12 people.
Two Rooms and a Boom. I have to agree with the other people here, it’s pretty great.
Cat On Yer Head is also fun (and totally free, mostly), but you need something like 30-to-180 or more people to play it.