I've been certified for about 11 years.
Most of my diving has been in Mexico. I would love to dive some of the exotic locales mentioned (South Pacific or the Red Sea would be incredible), but the airfare alone costs more than a whole trip to Mexico...
I was certified in Cozumel and I've been back to Quintana Roo six times since. The last three times we never even went in the ocean, we did all our diving underground. Cenote diving is a unique and incredible experience, I'm hooked! One highlight was snorkeling in a Mayan Sacrificial Well. We had to rappel down into the sinkhole after hiking through the jungle in a monkey preserve.
I have also dove a lot in the Puerto Vallarta area, mostly shore dives and around Los Arcos. It's been years, but I have also dove on the Oaxacan coast.
Other warm-water destinations I've been to are Jamaica, Costa Rica, Nicaragua, and Hawaii.
I don't do as much cold-water diving as I would like to, as it is hard to find dive-partners (my wife draws the line somewhere around 70 degrees). I have dove countless lakes and rivers in Oregon and a few times offshore in the Pacific. I have also dove the Hood Canal in Washington a few times.
We mostly dive on our own (no guide/divemaster for about 90% of our dives). Cavern/cave diving is the one kind of diving that I wouldn't consider going without a guide - I like my life a little too much!
These are a few older threads; a couple general diving threads and one I posted last winter about some chilly diving at the local reservoir.
http://www.monsterfishkeepers.com/forums/showthread.php?t=266266
http://www.monsterfishkeepers.com/forums/showthread.php?t=209280
http://www.monsterfishkeepers.com/forums/showthread.php?t=121258
Here is a shot of my wife rappelling into the Sacrificial Well and one of the 200+ skulls that littered the floor of the cenote:
