Tradeshows - what, if anything, to give away

We are about to gear up for one of the annual trade shows we sponsor each year, the Summit on Customer Engagement. Still deciding if our booth (really it’s a table) should have a giveaway.  One year it was mood pencils, when you held them the pencil color changed from black to bright blue.  Quite a conversation starter!  Another year it was a booklet of post its.  One year we put sharpened pencils with our logo and url on the tables in the main conference room, a way to get our name out to everyone, even those who didn’t stop by our table. We want to avoid the give aways that are just fun toys for the kids, we’d rather have something attendees keep and find useful, and of course at a reasonable cost.  Pens, lanyards, business card magnets are just a few of the items that come to mind.  We do know who we’ll order from, we’ve had great success with 4Imprint, we’ve like the ordering process and quality of the products.   Do you see company value in tradeshow giveaways?  If so what’s your favorite?