Traditionally hotels in cambs were crap or expensive or both
If you can get a deal then the university arms and the regent are both pretty nice and central. The garden house is nice but usually really expensive.
There is a travel lodge near the train station and a premier inn and travel lodge out at Histon on the main bypass road that are the value options.
I've recently stayed at the Doubletree by Hilton in Cambridge. Superb hotel with large, stylish spacious rooms. It's also the only hotel that backs onto the river. It's not cheap though, and I'm not sure on their photography policy as I was there with my wife.