This is from my research a while back. They are listed in order of perceived quality (i.e. the best at the top) -- this is just a perception thing based on research (a combination of the forums, the company websites, and speaking to them on the phone), not experience. Matt Ball from Rimfurbish is a really nice guy. I haven't used any of them though. Also note the prices are very specific to the wheel type (hence my description below).
18" Monza II from VW Golf GTI
Diamond Cut Face, Anthracite Infills
Rimfurbish (refurbished the tyres of the obsessive blue M5 owner)
http://www.rimfurbish.co.uk/index.html0121 525 2525
Matt Ball
£70 + VAT per wheel
£7.50 + VAT per wheel to strip and refit tyres
£30 + VAT total shipping (all journeys)
Lepsons
http://www.lepsons.com/home.phtml01634 580582
£68 + VAT per wheel - 7 working days
£90 + VAT per wheel - Leave whole vehicle, 2 working days, booked solid for several weeks
Have samples in their showroom to decide whether their Diamond Cut is close enough to the existing wheels
Spit & Polish
http://www.spitandpolish.co.uk/01732 367771
£62 + VAT per wheel - 5 working days, or leave whole vehicle, 1.5 working days, booked solid for several weeks
Pristine Alloy Wheel Refurbishers
http://www.pristinealloywheels.co.uk/01908 282628