small world is definitely worth the price of admission. Munchkin is a lot of fun, it's really easy to get nontabletopers to play also. I have the cuthlu, zombies, space, pirates, and superhero munchkins. They used to get a ton of play time but since we started gaming more they seem to take up a lot of dust. Me and the wife get games of small world in while the baby is sleeping and when he goes to bed at night so that gets a ton of playing time for me anyway.
The wealthy of expansions is something which puts us off actually. MY friends are the type that feel they have to get everything associated with something they love. It may fall to me to buy it.
I have to ask, where do people usually go to find some of these games (other than online)? The big stores like Walmart and Target usually only have the old boring standards like Monopoly, Life, etc.
Although we do have Carcassonne and Monty Python Fluxx, and we enjoy playing those. (Well, we enjoy them when we can convince the kids not to take everything personally!
Mostly online, but we have a chain of shops called Forbidden Planet. After Tabletop gained popularity we noticed the board games they played started appearing in Forbidden Planet.