Choosing a gift for beta testers

We are almost at the end of a very successful beta phase. Now I want to show my gratitude to best beta testers who helped us. (many of them are potential clients as well ).

What do you think would be a good gift, something that they would want to show off in their blogs or to show off their colleagues. Obviously we can't be too generous as we haven't even sold a unit yet. Some ideas:

• A cool gadget (maybe from thinkgeek or something like that )
• A limited t-shirt (with some cool slogan on it )
• Just bunch of lovely "thanks a lot" cards to lots of beta testers

We got budget of 500$ we can either get something big to one person or get lots of stuff to many people.

What do you think? What would you do? Also do you think this is a good use of money or just burning it?

P.S. We got the limitation of shipment as well, our testers are from all over the world. It should be something easy to ship.

I don't know how many users you have, but how about a high quality t-shirt that says something like

"I helped beta test zyz.com and all I got was this stupid t-shirt. "

It's so tacky that it might be kind of cool. I'd get a kick out of getting something like this. ;-) And if it was a good quality shirt, I'd wear it.

But more importantly, when they wear it, everybody they know will ask them about it, and they will verbally promote your website.

Is there any way you can kill two birds with one stone and make them promote your product even more?

For instance, you could give them invites (free product) that they can give away to their friends. This way, they'd feel empowered, and they'd actively promote your product. That's how Google does it (think Google Voice and Gmail invites).

This approach of course would only work if the product itself is something that friends of beta users would find useful.

I really hate to be a downer because I think this is great idea, but the fact is that many companies have a policy against receiving gifts. It's rarely a problem at small companies but if it's "enterprise" it's possible.

But I voted up some answers above because they're good. :-)