The former Balloch Central station building is now used as a tourist information centre:
Sticking with Strathclyde/Greater Glasgow, the former Bridgeton Central is now a newsagents (was formerly a Ladbrokes betting shop):
And finally, the original (and utterly magnificent) St. Enoch subway station building (grade A-listed to boot) is now a Caffe Nero branch (was formely, like Balloch Central, a travel info cente). Yes, this one is a slight cheat, with the station itself still being open, but it's also one I just couldn't ignore:
I realize that these aren't nearly as unusual as the ones already listed above, but this nevertheless is a interesting cross-section of possible station building re-uses.