@Bigshot ,
Coffee is ageless (well, don't take toddlers out for it, but you know what I mean). Coffee can end up as not a date, and everyone saves face. Drinks pretty much 100% = date.
If you're looking to minimize ambiguity, ask her out for drinks. If you want to provide an out in case you aren't on the same page, ask her out for coffee (and then, if it goes well, ask at the end, "I'd like to see you again. You, know, for a date." Then the ambiguity level is at zero).