This looks like an agamid species.The picture is not very clear though, so it's not very easy. Wikipedia does have a list of agamid species in Singapore, making this a lot easier! Calotes versicolor is my not very educated guess. Could also be one of the Draco species (Flying/gliding lizards), though I think these are far less common, especially in civil areas. I'd say look at some pictures and you might be able to figure out what lizard this is yourself.
http://en.wikipedia.org/wiki/List_of_Singapore_reptiles#Family_Agamidae_.28Agamids.29
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