OK, heres my 2p worth...
We have a Dell 5110cn Laser, and I bought it based on excellent reviews from Computer Shopper and elsewhere. It is essentially a rebadged lexmark, but dont let that put you off - its superb. It offers duplex printing, the driver gives you the option of password protecting the colour option, so if you only want staff print in colour, just set a password.
http://www.pcpro.co.uk/shopper/reviews/92553/dell-colour-laser-printer-5110cn.html
The outlay for a set of original toners is high - high capacity rainbow pack retails at around 550 quid from Dell, but they last well. If you shop around you can get them much cheaper. I have a contact at a company called Wordflow, Philip Warr. He can do the pack for closer to 400 quid.
http://www.wordflow.co.uk/pgIndex.cfm?sitevar=reset&appvar=3494
Also, if your felling adventurous and in the mood for saving even more money, you can refill the carts as they are literally just plastic cylinders full of toner - no other gubbings inside like drum etc. I have bought a kit from TonerTopUp, which is excellent. It cost 10 quid has everything you need to melt a hole in the cart. The toners themselves are 79 quid per color and 16 quid each for replqcement chips. Strangely enough, they couldnt do the black at a lower price then the dell original, but its only 56 quid. Saves a fortune.
http://www.tonertopup.co.uk/productCatalog.asp
I have no link with either of the companies! Just wanted to spreaad the word. You wont be dissapointed if you use either of them.