Here are some links to useful advice pages for house hunting and housing and also the links to estate agent websites:

Housing advice:

Shelter - http://england.shelter.org.uk/get_advice/advice_for_young_people/students 
DSU Accommodation Office - 0191 334 1770/4

Estate Agent Websites:
Durham Student Pad (lists all DSU Approved Landlords' properties - including private landlords) - http://www.durhamstudentpad.co.uk/
Accommodation for Students - http://www.accommodationforstudents.com/Durham.asp
D & J Franks - http://www.studenthomesdurham.co.uk/
Student Home Zone - http://www.studenthomezone.com/
Robinsons - http://www.robinsonsestateagents.co.uk/durham-student-accommodation
CRM - http://www.crm-students.com/en/student-accommodation/durham
Q Student - http://www.qstudent.com/
Bill Free Homes - http://www.billfreehomes.com/
Homes for Students - http://www.homesforstudents.co.uk/north-east/county-durham/student-accommodation-durham
Club Easy - http://www.clubeasy.com/
Right Move - http://www.rightmove.co.uk/property-to-rent/Durham.html
Bradley Hall - http://www.bradleyhall.co.uk/
Hope Estates - http://www.hopeestates.com/
Rise Lettings - http://www.riselettings.com/
Even More Properties - http://www.evenmoreproperties.co.uk/
Student Accommodation 4 Durham - http://studentaccommodation4durham.co.uk/
Harringtons - http://www.harringtonsdurham.com/
JW Woods - http://www.jww.co.uk/

If anyone finds a good site with lots of good houses on there or if any of the links don't work - please email me!