What I did after getting my PPL is 10 hours or so of cross countrys just so as I could enjoy flying whilst only having the pressure of conducting the flight safely rather than the pressure you get when building up to the skills test.
Longer term an IMC is a good challenge and it will certainly sharpen up your flying skills and it may get you out of trouble one day.
Aerobatics is also fun and again will sharpen up your aircraft handling skills and make you a better/safer pilot.