and again for PowerDevelopments in Basildon, they have done a great job on my brothers 3 series and great prices. i have not used then as i have not needed anything on the Z4 yet but they would be the first place i would go if i do.
I agree on the friendly service, top blokes infact but they made me wait well over a month for some brake discs for my M (which i desperatly needed as it was dangerous) when they did turn up they were the wrong ones as they had ordered M3 discs as they didn't know i had Csl discs on there, also Had a rattle on the drivers side front wheel, they said it was a "normal sound" sounded like someone had left a spanner in the wheel arch, not normal to me. Took the car to the new Indy after a reccomendation from a friend and the car was done within a week, fitted the discs, pads sensors checked all around the wheels and surrounding areas cured my rattle and only charged me £45 for it all.
But... When i had my 3l coupe they were very helpful, maybe they not to good on the M stuff I guess.
Not quite essex, but if you're willing to drive to Bexley (just by dartford) you can find BM Sport, which looked after my Z4 well.
It's an BMW specialist garage, and I would recommend it to anyone.
Powerdevelopments always seems to get good reviews although i havent used them. I did consider Bennets but they seemed very expensive. Pretty much main dealer prices.