If you wanted a good workhorse then the HP LaserJet P2015 would be good but its a bit pricey at £170 -£210 depending on what version you want. The different versions have letters after the code, n=networking, d=duplex (prints on both sides of the paper). We use the P2015dn (prints on both sides of the paper + network) at work at it's been faultless.
A slightly more economicly priced one is the HP LaserJet 1020 which shold be fine for normal letters. Thats ~£50 but its nowhere near as fully featured as the P2015 (no networking, prints at a lower res, slower at printing etc). But would be good as an entry level option for a small office.
A good non hp printer is Samsung ML 2571N but i can't personally vouch for it as i've never used one (our office is all HP and i use a canon mfp at home). It has networking and comes in at ~£160 or the basic Samsung ML2010 at ~£50 with again with the lower feature set.
The other thing to bare in mind is the cost of toner. HP toner is quite expensive but you usually get more in each cartridge.
i would personally spend the extra cash and get a P2015n and have peace of mind that you have a bullet proof printer that can grow with the business.