In no particular order:
It all depends on your language ability, your comfort level in travelling alone, and your ability to "wing it" versus having a pre-planned agenda.
1. Costa Rica. Relatively easy for a single guy to go without a plan, without much Spanish and still have a good time. Easy to meet local working girls, tougher to meet regular semi-pros. Relatively safe with just the usual common sense precautions. Inexpensive once you get there.
2. Domincan. Very similar to the above, darker skinned ladies, a well organized "monger" community at The Palace in Sousa where you can meet up with other like minded travellers.
3. Brazil. From what I have read, probably a bit more expensive on average compared to Central America. However, its also safer especially for someone who does not communicate fluently in the local languages. Women are perhaps less "downtrodden" and a bit more glamorous and naturally hot, as are Columbian women.
4. Cuba. Never been. Canadian vacation hotspot not yet open to Americans. Enjoy it before we ruin it. LOL! Local crackdowns on prostitution vary, prices are still among the least expensive anywhere.
5. Thailand and the Phillipines. Do alot of research. A mecca, but with popularity comes pitfalls. Talk to veterans and check the sites like WSG to find the best tips.
6. Eastern Europe and Russia. Not inexpensive and there is a language barrier. You can find ALOT of regular normal girls who work one or two days per month simply to make rent money. The best part is that you can make ALOT of connections in advance over ICQ or MIRC chat programs. Big dividends if you are willing to invest some time in advance.
7. Amsterdam and Germany. Again, I dont know much about it. Probably inexpensive to get there, but more organized and less random. Good for someone who needs a plan.
8. Organized destinations like Viking Resort. Expensive but a slam dunk at a nice facility with no guesswork.