I recommend a good font management tool like Adobe Type Manager. This way you can have hundreds of TrueType fonts on your system and turn them on and off as needed.
Any TrueType fonts that are active will be useable in Vegas. Stay away from Postscript(Type 1) fonts, they can't be used with Vegas.
There are many places to get free fonts on the web - I like www.chank.com for some cool designer fonts.