Continuum 1st - 4th August 2008 in Leicester, UK.
Tentacles Convention - Welcome! 9th - 12th May 2008 at castle Stahleck, Bacharach, Germany (yes, it is held in a castle)
Both are heavily Chaosium based, Tentacles is more CoC oriented than Continuum, both have RQ and Glorantha and HeroQuest. There are board games, RPGs, Freeforms and all sorts of goodies.
I went to Tentacles for the first time last year and had an absolute blast. I used to go to Convulsions, the forerunner to Tentacles, but had a spouse-enforced break for a few years, but I've been to the last 2 Continuums and they were pretty good.
If you like BRP-based games, have a free weekend and can stand being around like-minded people (i.e. geeks and nerds, myself being an obvious exception which is why I am on this forum at 12.40am
) then they are well worth going to.
If you do sign up to Tentacles because of reading this and haven't been before, then put my name "Simon Phipp" as the person who introduced you and I'll buy you a drink or two .......