Here are some that I like:
- NewBlueFX has more video FX for Vegas than any other provider. Really quality stuff and plenty of it at a reasonable price.
- Boris FX has several nice plug-ins to Vegas. It has a much steeper learning curve though.
- Pixelan is one of my favorites. Some nice motion FX and transtions
- proDAD has a nice collection of FX as well.
There are more but those are the main ones that come to mind.
~jr
http://www.johnrofrano.com
http://www.vasst.com