You'll be doing them a favor to get them glasses they can actually use for parties or regular dinners. For me, that means something they can replace as they break, so anything not available from a department store, Williams-Sonoma, or something like that is out. Feel free to source them from wherever you prefer, but it should be something they can buy more of. I think that rules out any of the specialty glasses available via geek catalogs, leaving Riedel and maybe Spiegelau (they're available on Amazon, so I consider them mainstream)
Then, if you've got the budget, I would get a set each of water, sparkling wine, white wine, and red wine. Looks impressive on the table. If you've still got the budget, throw in a decanter. It would be quite the present.