The more traditional ones that I would recommend:
Tao Circle, Tai Chi
tao circle tai chi
http://taocircle.com This group is lead by a former teacher of mine, Bill, who now lives in Denmark. Together, this group has very deep knowledge. They tend to mostly practice forms though and very little application. You can find a couple of articles from Bill on the page.
Baji and Tai chi:
http://baji.se/blog/Lu Baochun lives in Finland, but this is he Sweden group. You can find many fine vids with Lu on the Youtube.
They also have Yin Bagua from He Jinbao.
Per Nyfelt, Sun family martial arts, student of Sun Jianyun. Don't know if he has a tai chi website.
(Edit: Faxing provided it below (funny that I didn't find by googling...))
There's also traditional Wu/Hao Tai Chi that seems very interesting. I haven't visited that group though. There are more groups and teachers around, but I wouldn't be willing to recommend the other ones I know about.