http://www.singaporebikes.com/
Register for the forums. Go into the bikes for sale area and prepare to be overwhelmed with selection.
Take your time, probably a good idea to go to a new bike shop to decide on what you want. Scooter through Roadster, it isn't easy to just say 'I'm going to buy a bike'.
I took 2-3 months watching the sale site getting an idea of what was out there. Then took a month testing out Honda CB400's which was what I decided to get.
Do you have licensing? 200? 400? Open? Your license will determine what size bike you get, then you look at model. I have open license but my wife decided on the size of my bike. She thinks a 400 is less likely to kill me than a larger bike??? Go figure
But I'm happy with a 400 for city riding and my days of long treks are long past.
The site above is an incredible resource (the forums are where the citizens hang out - the site itself is vendors). There is a huge number of classifieds for 2nd hand bikes - overload but incredible for selection. Ask, or PM me if you have questions.
And Sg is a great place to ride, hot as hell, but still really nice.
Cheers,