Sony Vision Series is a nice collection of moving backdrops as does Digital Hot Cakes if you just want to buy some. Main Concept also has some free background loops on their web site and ones for sale.

As for a plugin that could generate some, probably the greatest one in Vegas 4 for this is the Generated Media Noise Texture. Just keyframe the progress parameter and you can get some really nice moving backgrounds.

If you want a program that will generate them for you, I have a tutorial on my web site on how to use Axogon Composer to make the same loops that are found on the Main Concept web site. Axogon is a freeware beta of the Main Vision compositor that MainConcept sells for $259. It’s getting harder and harder to find it on the net but its worth the search. Just follow my step-by-step tutorial and you’ll be generating your own backgrounds in no time at all.

~jr