http://www.clickflatshare.co.uk/
http://manchester.gumtree.com/
http://www.homes4u.co.uk/
http://manchester.spareroom.co.uk/

hola, I got the following tip concerning housing in Manchster:

http://www.manchesterstudenthomes.com/ (they have a section for single semester housing) or just look at the ‘available’ tabs.

Most students live in Fallowfield or Withington which are both pretty fun places to live. You could also look at Rusholme (the curry mile), West Didsbury (a bit more expensive and far from the centre but a really nice atmosphere), Chorlton or around Victoria Park area. And all the bits inbetween!