Two places I use
1) Sesame Electronics - nothing flash, about hobbyist level (although on
occasion I have received superb PCBs from them) I suggest min 0.75mm Track w
0.5mm Spacing - a bit rough but good enough for most bar the more complex
prototypes and very reasonable pricing.
http://members.tripod.com/~sesame_elec/
2) Printed Electronics - Superb work -they would manage 0.25mm Tracks
(although the minimum I go to is 0.5mm which they do with ease) however they
do cost quite a bit more (around $300 odd for an A4 panel - 1 off if memory
serves).
http://www.printedelectronics.com/ Cant find the details to contact Mike
Lynch who makes the PCBs but they usually have an ad in the back of Silicon
chip