I was in Singapore in the last few weeks for a 3 day stay, and had some good fun there. All kinds of women can be found there, for the most part, and there's different types of service available. Here's a short breakdown of Singapore action from my research:
Geylang and other brothels-
This is the only legit means of hobbying in Singapore, to my knowledge. Apparently Geylang used to be mainly Malaysian women, but with their standard of living going up, many of the girls being brought in are now Chinese -- interesting with all the human trafficking discussion going on right now that the Singapore government is essentially officially condoning such trafficking, as these Chinese women get 2 year visas to do nothing more than service guys in brothels.
I think the closest MRT station is Aljunied, and you can either take a cab or walk from there depending on how far you are going. There's a bunch of shops and restaurants on the 'odd' streets (Lorong), and the brothels are on the 'even' streets. Depending on the type of house, the price goes from S$50 to S$150 for 45 minutes/1 pop.
Street walkers (Geylang)-
These girls are not legal, and aren't required to be tested, so buyer beware. I've read that there was a big crackdown on these girls in the street so there might not be nearly as many of them. Prices vary depending on the girl, and usually condom and room is not included. There's temp-stay hotels on virtually every block in the Geylang neighborhood, so you are covered.
In-call agencies-
There's a bunch of orgs that run girls out of apartments in Singapore. These are also not legal, and I think the vast majority of these girls are Thai, although in my research I saw a few that are also Korean. The places are fairly upscale and secure, although as part of the multi-call system, they usually direct you to an HDB building, which is gov't subsidized housing in Singapore-- the majority of residents live in such housing, but as a foreigner taking a taxi or whatever you might get a bit of a strange look asking to go to 'Block 25 on such and such street'. They do this because parking is sometimes tough, and the public housing usually has some available parking, and they want to make sure that you aren't showing up early and spooking the neighbors at the actual complex. Once you get there, then they direct you to the real location nearby.
Most of these orgs have pics of the girls online, and many offer things like nuru massage and tarma (threesomes with 2 girls).
The bar scene-
The two places to be for this are Orchard Towers- the 'four floors of whores' and Brix, which is in the basement of the Hyatt hotel. Both of these are right off Orchard Street, which is one of the major shopping complexes in Singapore. In fact, Orchard Towers is right across the street from an Armani store and the Hilton. It's really not 4 full floors of whores, though. There's lots of other stores in there, especially tailor shops etc. From what I've read the place to go there is Ipanema on the 2nd floor. Most of the girls there are vietnamese, and you can negotiate for short time (one pop) or long time (overnight). I didn't spend any real time here during the standard evening hours that the girls are there, so I don't have much to report, and I didn't go to Brix at all (which is a night club where the women are supposedly very hot, and with a higher asking price).
There's a bunch of options for fun in Singapore, and if it weren't so hot and humid there all the time it would be the ultimate paradise for hobbyists. Hopefully the above info helps you in the future- I'm by no means an expert but let me know if you have any questions and maybe I can help.