The Financial Times - www.ft.com/arts/crossword - has a good prize cryptic (often set by Mudd, who is the same setter as the Guardian's excellent Paul) and general knowledge Polymath on Saturdays.
The Times - thetimes.co.uk - has the easier Times2 puzzle as well as its more daunting main one. Another very good general knowledge is Prospect magazine's monthly Gneralist puzzle (www.prospect-magazine.co.uk) Good luck/