Here is a set of 11 brushes for Adobe illustrator. They have nice swirls and gradients. By changing their colors the possibilities are endless! (the only limit is yourself ;)) There is a thorough helpfile to show you the possibilities of changing the brush settings including pictures of the effects.
These are perfect for making backgrounds or anything else you can come up with.
Note: the helpfile tells you how to install the brushes. Make sure if you use winzip for example, the filename stays the same. If it prefixes the file with ’.-’ delete that, because it might give an error trying to load the brushes then.