Just a quick note, here's a list of conventions in Southern California for the rest of the year
~~Although it's over now, the first May of every year is free comic book day! Most comic book stores participate.
AM-Squared: June 15th-17th at the Anaheim Convention Center. Haven't been personally, but I've heard great things about it. It's the same founders as Anime Expo.
Anime Expo: June 29th-July 2nd at the LA Convention Center. The convention to go to for anime fans apparently. I haven't been since they moved from Anaheim due to a waning interest in Anime/Manga, but it's THE convention to go to for Anime fans
Stan Lee's Comikaze Expo: September 15-16 at the LA Convention Center. It's the second year, and Stan himself is now the official sponsor! Much smaller scale, but a super friendly atmosphere.
Conjecture: October 5-7 at the Town and Country in Mission Vallery: I think it's run by the same people as Anime Conji, although it's theme leans more toward scifi/fantasy.
November 3rd-4th: Long Beach Comic Con at the Long Beach Convention Center. I LOVE this small convention! Already have my hotel booked.
There's also Mickey's Not So Scary Halloween Party at Disneyland, a ticketed which allows anyone regardless of age to dress up at the park and includes special events, rare character meet and greets, a Halloween parade, and trick-or-treat stations.
Hope this helps!