Cruising is fantastically mega-awesome. Lots of people dive and lots of people cruise, so I'd guess that if you look around you can find cruises which can specifically accommodate diving. Maybe a ship that arrives early in the day and overnights at a certain location. Lots of cruises do this (and it's great).
If you have an old fashioned travel agent that you like, they are usually a great resource for cruising, and cruises are the same price no matter who you buy them from. Travel agents are great in this regard.
Two great resources for cruising research:
www.cruisecritic.com - a forum like this is the cornerstone of this - they may be able to help if you search.
www.vacationstogo.com has all the pricing for cruises. It's updated all the time.
I LOVE cruising and want to do it again! I've never dived on cruises but done lots of snorkeling. Just have to save up for it.