Mark, I have been to kona several times. Personally, I would recommend these dives (in order of coolness).
1) shore dive at place of refuge (aka two-step). Very easy entry and one of my favorite dives in all Hawaii.
2) black water dive. This is a different type of dive, but truly amazing. It is one to put on a bucket list.
3) shore dives off puako with Jackson Seay (divepuako.com). He is a great guide and puako is an awesome site. Try to get out early before the afternoon swells hit.
4) manta night dive. I have done this a few times and been happy every time.
All four dives are completely different, but each beautiful in there own way. You will have seen the best (IMO) of the big island.
Have fun!
---------- Post added January 29th, 2013 at 10:23 PM ----------
BTW- I dove with Kona Honu and Big Island Divers, both are top notch operations.