I only know a couple of conventions over that side of the pond off of the top of my head and wondered if people could name others?
I'd love to go to a convention over there in years to come, but I have no idea which are the good ones and which are the bad. xD

AnimeNEXT and Katsucon were recommended to me the most by friends over the pond.

Which area were you thinking of? There are probably hundreds of cons there so we could be here a while if we listed them all
It's probably best to choose a con based on an area you would like to sight see at the same time, for example if you want to explore New York or something. Then we can go from there in suggesting USA/Canadian cons. If there are several, then name them!

I haven't actually been to any yet, but would looove to go to AnimeNEXT at some point. New Yoooork *A*

I'd probably wanna go to CA or NY or something. I've no idea really, I just don't know what the really big cons are over there.

The ones I know about are

San Diego Comic Con
Dragon Con
PAX Prime
PAX East
Wonder Con

It really depends on what you mean by Convention.

Well mostly anime/manga really, but I posted this for all to use as well.

I went to Anime Detour in Minneapolis in April, and i intend to go again this coming April. its a pretty decent convention, and really friendly

I pretty sure (but don't quote me on this XD) that Anime Expo and Otakon are the 2 biggest cons over there that centre on Anime and Manga solely.

I've seen loads of fan vids and convention schedules for past Anime Expo's and it looks amazing. I have set my heart on attending that one as soon as I have saved enough XD

I also want to attend Dragoncon it looks like so much fun with such a mix of fandoms!

Anyway I'm rambling now XD

It's my dream to go to DragonCon ;~;

I was looking at people's costumes on here once and saw a costume from DCon 2011 and I thought, I don't remember seeing that at D-Con, then looked at more of the pictures and realised that it wasn't Dundee Union's D-Con, it was DragonCon haha

SDCC is AMAZING!

There are hundreds of conventions over there.

Here's a website that lists some of the major ones: http://animecons.com/events/

I've been to Metrocon in Florida and have to say that it is amazing.

These are the conventions I've heard quite a bit about (sorry if they've already been mentioned xD):
Yaoi-con
Sakura-con
Anime Boston
Fanime
Katsucon
Sac-Anime
EXP Con
Youmacon
Shadocon
Otakon
Ikkicon
Ohayocon
Megacon
Anime Central
Anime St. Louis
A-Kon
AnimeNEXT
San Japan
AnimeFest
Dragon*Con
And of course Metrocon as mentioned earlier~

And those are the main ones as far as I know, though you'd have to ask an american cosplayer about more specific ones in a State. I know there are between five to ten in Florida alone, so there will definitely be loads more in places like New York and California.