I find that the Spyderco Triangle Sharpmaker (about $50-60) is very effective and versatile. It is a sophisticated version of the simple crock-stick type system that provides an easy and effective method for controlling the angle of the edge. It is not cheap, but I think almost anyone who takes the time to either read the directions or view the included video could soon confidently put a great edge on any knife and even scissors and other non-knife cutting tools.

It comes with 2 sets of ceramic stones of different coarsness and you can optionally purchase an even finer set and/or a coarser diamond-coated set. These are not necessary for good results, but makes the system even more versatile and gives you options for specialized applications. The optional diamond set is nice for speeding up the major sharpening jobs that require deep re-profiling of the edge (to remove chips or correct abused edges).

Good luck.