Here are some (probably outdated) links.
Banner URL Description
Mostly Virtual-On related
Virtual-On HP http://virtual-on.dricas.ne.jp/oratan/index.html The official Dricas page for Dreamcast Virtual-On: Oratorio Tangram.
Ver.5.66 HP http://virtual-on.dricas.ne.jp/oratan/hotstart/msbs566/index.shtml Official Dricas page for Virtual-On: Oratorio Tangram Ver.5.66.
Virtual-ON Customize Factory http://www.geocities.co.jp/Playtown-Toys/2489/ An essential site if you want to make fantastic custom VRs.
VMS Tools, etc. http://homepage2.nifty.com/kamino/ Has the best Windows-based VMS software (for general use), among other things.
Yahoo! Japan Auctions http://auctions.yahoo.co.jp/ A good place to get Virtual-On related goods.
GameFAQs http://www.gamefaqs.com/ A good place for VOOT FAQs, and it has a popular (relatively speaking) message board.
SYDVOC http://www.sydvoc.com/ Has a (relatively) popular Virtual-On message board.
APX http://www.geocities.com/aphxero/voot.html Homepage of Mark Gehr, AKA APX or ApharmdXero. He's an AVC player in Washington state.
AVC http://dsn.itgo.com/vo/ Scott Robinson's Virtual-On page for Auburn Virtual-On Crew, aka "AVC".
MCT http://evenpar123.tripod.com/ EvenPar123's homepage for MCT.
Not Virtual-On related
trillian http://www.trillian.cc/http://www.trillian.cc/ Awesome Windows-based chat program. Combines ICQ, IRC, AIM, Y! IM, and MSNM into one program.