You can probably get a list of official agents from the Singapore Immigration site. Getting a visa is simple. All you need to give is your tickets, and Passport. Though use a trusted agent, since you will surrender your PP to them. Which is gold here in India. I explored Singapore for three weeks:
1. Singapore is an artificial state. So you will not find historical monuments or archaic buildings like our Red Fort, Taj Mahal, or even VT Terminal. Everything is fabricated and man-made.
2. It is chronic for cleanliness. So do not litter, spit, or even get off the plane with chewing gum in your mouth. Be really careful about your litter.
3. Get a Metro Card as soon as you can. That is all you need for travel....! Top it up with SGP 100 or something. Why..? You can use these cards in the metros (SMRT card), buses, KFCs, McDees. Even at small utility shops. Basically anywhere where you see an MRT logo, this card will work. Some cabs also use these cards. You can ask before you board. I bought a calling SIM card using an SMRT card..! Even cigarettes and beer at utility counters can be purchased using SMRT cards.
4. Pick up a map from the Metro Station or airport. This will help you get around. SGP metro has a well connected 'circle line' which links all metro lines.
5. Carry water in your bag when you travel and save on expenses.
Now, SGP is a land of malls and malls and malls. Probably shopping: is a national hobby / pastime there...! Actually that is all there is. So off course you should avoid that. They are quite expensive in nature. When you go to foreign locales, always and always try to do different activities than your home-land. That is what I feel...!
1. Visit the Botanical Garden. The metro line leads literally to the gate of the wonderful garden. 4-5 hours.
2. Visit the zoo (see the route on the map, but I think you have to metro + bus). You will get to see white tigers, maybe an elephant safari, and they can take you on a boating trip which is really cheap. 4-5 hours.
3. Visit an island called Pulau Ubin (again metro + bus). You mount a ferry from an end point (bus), reach the Island, rent a cycle for ~SGP 10 and bike around. It is really fun. Have some local food there, and come back. One day trip.
4. Avoid cryptic and shady places like: Little India (you basically get Indian goods there and Indians selling gold, and why would you want to bump into Indians abroad), Little China (over hyped flea market), Boogeys (another cheap run-down place), and Mustafa. Believe me, Mustafa is just a mother-of-all go down / silo; selling piles and piles of stuff. I found it a waste of time, rifling through shelves of jeans and shoes to see what I want.
5. Visit Orchard Street (Red Line I think), and browse the malls quickly. Do not waste your time in malls.
6. Museum - is quite good and informative for history. Read up about how Tamilians migrated to SGP and became money-lenders. Also SGPs WW2 heritage.
7. There is an old Armenian Church on Hill street. It is near the museum. That is good to see.
Else, just go where your nose and instinct lead you. Have fun..! Remember us..!