These are the ones I know:
Japan Expo (Paris / France): A more than huge con (> 40000 visitors) because it's all about japan with a pretty cool AMV contest with lots of great videos from what I've heard. The contest is organized by the con staff itself and being screened by Fantasy Movies.
Connichi (Kassel / Germany): Pretty huge only anime con with some nice program and a contest since 2002. Unfortunately the rules are a bit stubborn and the screening last year had technical problems, but the ending celebration with all winners shown makes it up. It's being organized by MAGI2 and the AFT team.
Finncon / Animecon (various cities / Finland): A Science Fiction / Fantasy / Anime con mixed. Well worth visiting, pretty well organized.
Their contest is just plain awesome, I don't think any other european contest got such a great response: 900 people were watching the screening. This is by far the best contest I've seen yet speaking of organization and planning. It's being held by Venomi and the Arctic Tribe studio.
Wildercon (Cosgrove / Great Britain): I don't really know much about it, it seems to be well organized with lots of nice people and a decent contest which is being held by SD-chan.
Miniamicon (Southampton / Great Britain): Same as above, I only know what the site already says, they're based towards anything cute and so is their amv contest ^^
Conneko (Ludwigshafen / Germany): A pretty small con, pretty disorganized, but the contest rocked. It's been a while since I've seen so many great videos in a row, so this is the only point where the Animecon contest wasn't the best I saw
Unfortunately the preorganisation sucked a bit because the coordinator is damn lazy, but he got it all rolling in the end. This person is called The Motrix.AniMaCo (Berlin / Germany): Don't know anything about it, I just read that they'll hold their first contest this year, let's hope it all goes well.
There are two other contests in Germany but they're not worth mentioning >_> and I know that there is some contest in the Netherlands and one in Sweden, I didn't find out anything about them yet. So if anyone knows, please tell me
And I can't imagine Italy hasn't got some kind of a contest cause lots of great creators come from there, so bring em on
