The Virginia Flower & Garden Expo is this weekend (20th-22nd) at the Virginia Beach Convention Center. Tickets are $10 and kids 12 and under are free. There's also a $3 coupon off ticket prices.
http://www.vafgs.org/index.php

I think there was something in the paper a week or two ago about free soil testing kits available at the expo from the Virginia Cooperative Extension, but there is a fee for the actual testing. Here's a link to the online article:
http://hamptonroads.com/2012/01/get-dirt-your-soil

As for plant sales... I'm not sure. The Junior Virginia Beach Garden Club is having their 32nd annual flower sale. They're accepting pre-sale orders until Feb. 17th.
http://jvbgc.com/store/Default.asp

The McDonald Garden Centers have events too. They had an outdoor show last March, I believe. No idea when it will be this year, if they have one at all. Keep an eye on http://www.mcdonaldgardencenter.com/ and their events page to see what they have going on.

Oh, and before I forget again (I keep having to remind myself about this), there is a Virginia Beach Seed & Poultry Swap in March. Information...
Here: http://norfolk.craigslist.org/grd/2762191749.html
And here: http://seedswap.shutterfly.com/

If you're looking for sales at local retailers... I'm not sure about big sales. They aren't too consistent about that. I'd say just keep an eye out for sales at the home improvement stores, wholesale clubs (come summer they start marking their boxed plants down by as much as 90%... or so they did last year), and nurseries. Norfolk County Feed & Seed has very reasonable prices compared to the larger nurseries.

LOL, I was at the garden show this morning. And I plan to go to the seed swap in Pungo... Gina and I are members of the same gardening group meet-up which is being disbanded/adopted into this homesteading meet-up, which I love: http://www.meetup.com/VirginiaUHL/ I know people who went last year and they had great things to say about it, so I've got my heirlooms ready for swapping!

Will have to keep my eyes out for the rest. Thanks for the heads up.