Anachrocon in Georgia typically happens around the last weekend of February. http://www.anachrocon.com
The Alternative Living Expo in Philadelphia takes place around the first weekend of March. No website at the moment.
Wild Wild West Con in Arizona also happens around the first weekend in March: http://wildwildwestcon.com I might head out to this one if my schedule allows it.
Nova Albion in Santa Clara, CA usually takes place on the last weekend of March, but was canceled for 2012. http://steampunkexhibition.com/ Alas, this was one of the more interesting ones in 2011 with its Wild Wild East theme which had significant programming considering Asian approaches to Steampunk.
Steamfest in Atlanta, GA is usually around April 9-10. http://steamfest.blogspot.com/
Gaslight Gathering in San Diego is May 11-13th, 2012. http://www.gaslightgathering.org and I'll most likely be making a showing here.
Nakamacon in Madison, Wisconsin. The last weekend of May. Their website is down at the moment: http://www.nakamacon.com
The World Steam Expo in Deerborn, MI is usually the last weekend of May. http://www.worldsteamexpo.com
San Diego Comic Con is July 12-15, 2012. Not all steampunk but it's a don't miss. I'll be there. http://www.comic-con.org
Dragon*Con in Atlanta, GA is August 31-September 3rd in 2012. http://www.dragoncon.org
SteamCon in Seattle, WA is mid October. http://www.steamcon.org
TeslaCon in Madison, WI is around the week before Thanksgiving. http://www.teslacon.com
If you know of any other events or activities that might be of interest, drop me a line!