The bush is so full of these little drab birds that are difficult to identify. Usually they are little grey ones, but this one is slightly brighter than grey, with a beak that appears to be a slightly out of alignment and beady little eyes.
When I am feeling more academic I will consult my field guide. For now I'll just enjoy it for what it is - a little olive drab bird.
UPDATE - 17 September 2011: I believe it is a Sombre Greenbul.