As a local may I recommend the Gallery Cafe [on the corner/centre of town, just up from the FIAT garage]. The filling station is a bit hit and miss. Had some bloody terrible cakes there recently.
The Strawberry cafe is nice, not too pricey. The cafe in George Fishers is also very good.
The Chalet in Portinscale is very very nice.
+2 for the chalet, just round the corner from my house. Opens early and consistently good. You need to head out to portinscale though, and that also gives you the options of cheap and cheerful nichol end marina, or smart and sophisticated lingholm kitchen, both good in their own way. In town, marienda or treeby and Bolton, or the one on bell close car park (coffee kitchen?)for more of a greasy spoon, vinyl seats sort of feel. Bad coffee there, though.
I like the spoon in the car park mentioned above for a full blow out, i m into the old retro cafes though and its a bit hidden behind the high st. Filling stn was good when i went but imagine its packed at weekends.