Its dirty because my Dad's friend picked it up with his greasy fingers! >:| I like to keep my bass clean like a Samurai sword. Of course, cleaning my bass with a cloth every morning is like a religious ritual. Anyway, will water do? Or Windex? Or some kind of other liquid?
For daily cleaning the ones mentioned already are great. For serious cleaning of really dirty basses use naptha. Then guitar polish afterward. The naptha will get old polish, dirt, grime, spilled beer (trust me on this one), and other sticky stuff off without damaging the finish.
I used windex on mine the first few times and I was told it would hurt it. Is that something true? Since I heard it i've not gone near mine with anything for cleaning.