Here are a few of the SWAG products I've invested and an overview of their impact:
Character Cards:

Val Cox (http://www.valcox.ca/) illustrated Under My Skin and her gothic work looks GOREgeous in full colour. After falling in love with her illos of the UMS crew, I asked her to develop some unique SWAG to promote the book. She came up with three different cards based on the main characters, their personalities and a quote from UMS.
The cards are slick, hip and gothic - a great investment - worth the design and production fees. They also fit perfectly into the plastic, sealing bags used for the UMS chokers. Which brings us to....
UMS Chokers:

These choker necklaces were hand made by a teacher at my school who has a jewellery making business. She helped me locate the perfect crosses to match my vision of Eryn's gift from Alec, as well as the two strand ribbon bands.
I got a steal of a deal and only had to pay for supplies which made these stunning promo pieces worth the moola.
UMS Tees:
Made just for the UMS Launch Party (the live one in my home town and the online version). I had 24 tees produced - they were far too expensive but I LOVED them. Clingy and distressed/vintage, I adore mine and wear it often.
Worth the money? No. But as a cool keepsake you can wear with a cute pair of jeans/capris - priceless. ;)
UMS Postcards:
I had two separate designs created - one with the UMS cover and the other with one of the illos from UMS depicting the three main characters. I find the postcards most handy when mailing out ARC or prize winner copies of UMS - the large whitespace on the back lets me write a personal message. I had these printed at http://www.vistaprint.com/ - very affordable.
At bookstores, these don't seem to move as quickly as bookmarks...
Double-sided UMS/Second Skin Bookmarks:

I just got these babies. Double-sided bookmarks are lovely! Since VistaPrint doesn't have a template for bookmarks, I had to search the net for another printer. http://www.printrunner.com/ did a bang up job on my double-sided bookmarks, one featuring UMS and the other featuring Second Skin. Full colour both sides, one side with a high gloss, the other matte. Super affordable too.
These are hot items when I'm out at events and overall seem to get the most response.
I know there are tons of other SWAG options to explore, posters, banners, standing banners, buttons, magnets, pillow cases, tank tops, etc... and I do want to produce something specific for the release of Second Skin. I will have to ponder on this. In the meantime, good luck in your own SWAG adventures. I leave you with an image of some SWAG from authors who participated in the Crossroads Blog Tour this October:

You can see the UMS bookmarks resting on the brick wall. What a lot of loot, eh? If your interested, follow the tour in Oct 2011. Meet more paranormal YA authors and enter contests for amazing SWAG prizes.