The students of many colleges in Oxford will only have accommodation provided for them in their first or first and third years (although there are several exceptions to this: such as St Hugh's and Jesus) and therefore they move out of the city centre into private accommodation. This is also the case for students at Oxford Brookes where private university-owned accommodation is usually only available for the first year. The restrictions placed upon undergraduates (to live within 6 miles of Carfax) mean that this is generally restricted to the areas of Jericho and the Cowley and Iffley Roads.
The majority of students claiming to live 'in Cowley' actually live on the Cowley Road between the Magdalen Roundabout and Tescos (therefore being within a 1 mile radius of the edge of the city). Cowley itself is actually significantly further up the road and it's very rare for anyone to live this far out. Acoommodation may be cheaper here than most places in Oxford.
The Cowley Road is Oxford's equivalent of a cultural mecca. Sadly the Zodiac, with its regular local bands has been taken over by Carling and now looks much the same as any other big music venue. This has led to the cessation of popular nights like Fuzzy Ducks and the ska night, but does provide easy access to big names. There are still however possibly the widest variety of international takeaways you'll find anywhere in Oxford.
Jericho is often seen as the 'posh' bit of Oxford, and most students live on the Banbury or Woodstock Roads. Accommodation may be slightly more expensive but has the reputation of also being rather nicer.