http://www.apple.com/ipod/nike/

http://www.apple.com/ipod/nike/
Apple and Nike practiced Co-Marketing in the above link. Both company benefited from the partnership. For partnership to be successful both parties much befit from each other.
There are four main objectives of marketing co-operations
Build-up and/or strengthening of brand/image/traffic by implementing joint or exchange communication measures
Access to new markets/customers by directly addressing the co-operation partner’s customers or by using its distribution points
Increase of customer loyalty by addressing own customers with value added offerings from the partner - often useful for community building
Reduction of marketing costs by bundling or exchanging marketing measures
Co-Marketing is very nice provided both parties will keep to term.
This below is an example of multiple partnering.
http://www.skyteam.com/EN/index.jsp
SkyTeam is the second largest airline alliance in the world — behind Star Alliance — partnering fourteen carriers from four continents.
http://en.wikipedia.org/wiki/SkyTeam