According to a recent article in CNNGo regarding Asia's pornography laws, viewing and downloading pornography online in Singapore would not appear to be a punishable offense.
From Singapore's Media Development Authority's (MDA) website:
"The MDA does not monitor or track users' access to any sites on the Internet and does not interfere with what individuals access in the privacy of their homes. We are primarily concerned with the purveyors and distributors of pornography. Unless you engage in such activities, the mere act of visiting such sites is not an offence."
For those travelling to Singapore with computers, Singapore's Film Act laws make it clear it is not a good idea to enter the country with any questionable material saved on a computer.
"(2) Any person who imports any obscene film knowing or having reasonable cause to believe the film to be obscene shall be guilty of an offence and shall be liable on conviction -- (a) to a fine of not less than SNG$1,000 for each such film imported (but not to exceed in the aggregate SNG$40,000) or to imprisonment for a term not exceeding 12 months or to both; and (b) in the case of a second or subsequent conviction, to a fine of not less than SNG$2,000 for each such film imported (but not to exceed in the aggregate SNG$100,000) or to imprisonment for a term not exceeding two years or to both."
Read more: CNNGo.com