I can't think of any in Southampton off the top of my head, but I don't know that area very well. if you are prepared to travel then there are a few in the Meon Valley - Portsdown Hill, Butser Hill and Old Winchester Hill all spring to mind.
Or you could head off towards Winchester / Salisbury direction. There are a few on the Clarendon Way, such as Farley Mount
Edited: 09/01/2013 at 16:08