The web is all about customization and the Next Conference 2010 in Berlin offers to it’s attendees to make a personalized T-shirt of the event by integrating an online design tool from custom apparel printer Spreadshirt (I’ve used Spreadshirt in the past and their products are high quality and durable).
The Next10 website holds an embedded T-shirt design tool from Spreadshirt which has the event’s logo pre-inserted on the product and allows you to add text or other designs on top of that. While this move requires that you lose the creative control of how your logo is applied (but hey, people could do it by themselves anyway!), it stimulates a creative engagement with the delegates attending the event. The implementation cost should be low (I guess you just need Spreadshirt’s permission to embed the tool) so you can adopt this idea for your event too!