We arrived unaware that everything is done through agents here. We thought an agent was something for lazy people so we set out on our own and called up landlords about properties for rent. No one would call us back because we didn't have an agent. They just thought we were idiots. That was our first mistake!
After we got a good agent things were really smooth and easy. All of a sudden there were a lot more options on the table and we had someone to tell us things we had no way of knowing. Our Agent negotiated the rent prices (yes, they are totally negotiable), helped us through the letter of intent (WTF!). She drew up the lease paperwork and legal stuff that is simply not part of renting an apartment in any country we've ever lived in.
All that said, prepare to pay double what you would for a comparable place in the highest priced neighborhoods in North America. You have to adjust your expectations before you begin or it's very frustrating and try not to spend too much time comparing. People just seem to spend a much higher percentage of their income on basic housing here.
The above poster maybe had an unusually good agent. Normally they are not very knowledgeable or helpful, only interested in earning a quick buck, and are well-known for cheating (e.g. charging the tenant although the landlord engaged them - which is actually illegal). In my 12 years in Singapore, through five changes of rental, I usually gave agents a chance but always found the better deals (incl. all the ones I eventually accepted) without agent. It takes more effort, but that's worth for having a better place to live in the end.
"Letter of intent", all the other paperwork and "legal stuff" are not part of renting in Singapore: They were invented by agents to make it look like their services are needed. I never had any of that stuff - things are much easier and more straightforward if you talk to the landlord directly.