Two places I've used and would recommend:
Sollis Panelcraft, Harlow - They did my brother's Temper Zed repairs and it was a prefect colour match. Very professional, but friendly too. Make sure you go to Harlow not Chelmsford though, as the Chelmsford branch is gash.
Kraftwork Vehicle Refinishing, Chelmsford - Dav is a friend of ours, he carried out a front end respray on the Impreza that was flawless. He also quoted me an incredibly fair price on a front end spray for the 911, which I'd have taken had I kept it. He primarily works on Ferraris, Porkers, Astons etc, so high end stuff. Lovely guy, always very busy, but he'll be doing anything I ever need painting from now on.