In a thread on this in April 2002 Pocock & Shaw again came out top being universally recommended. Tylers were also strongly recommended.
A lot of other agents were mentioned in this thread which is worth reading in its entirety. Google has it here.
A lot of other estate agents are on the Web and a good place to find links to them is the Cambridge News property pages.
And don't forget to check out the Cambridge Accommodation Notice Board especially for rental properties direct from the landlord.