Alliances - do they work?

I visited a business friend recently and at the end of our discussion he offered me 4 cards.

Two were his own cards which he asked me to pass on to two friends. Good proactive request!

The other two were for a $2 discount on a coffee at a local coffee shop. Excellent alliance!

Why was the 2nd one so important? Because here was an opportunity for cross referring of business. Both parties benefit from this arrangement, as when I visited the coffee shop there were brochures about my friends Finance Business on display.

Alliances are a win-win arrangement were two people agree to actively refer each other business and have some visual stimulus for doing so (the cards and the brochures). In addition they often have a monetary stimulus as well. If I wanted a coffee why not visit that particular coffee shop and use my $2 card - it is a 60% discount.

So what specific and tangible alliances have you set up?