Book Yourself Solid written by:  Micheal Port

One of my absolute favorite  books on marketing your business. Here's an excerpt of his book on cross promoting.

This is one of my absolute favorite online marketing strategies because it allows me to partner with, and promote, other people I think are fabulous while they do the same for me. We've talked about how important it is to get other people to talk about you so you can quickly build trust with potential clients. Well, cross-promoting through marketing partners is the best way to do so. If my colleague sends out an email to her newsletter subscribers endorsing my services, products, or programs, her subscribers are more likely to trust me. When I promote her, the same will be true. It makes it much easier to build relationships with potential clients that way. It's just like meeting a great friend of yours. You love your friend and if your friend loves that person, you assume that person is great. The same goes for cross-promoting online (and offline). You can cross promote like this on many levels,: between you and another service professional who happens to serve the same target market or with or with larger associations and organizations. If you're an accountant who serves small business owners and you develop a relationship with the membership director for an online small business association that has 75,000 members and she promotes your services to their membership, just think all the of these new potential clients who turn into clients. The possibilities are limitless. This is why this is my favorite online marketing strategy. Here are some other strategies to consider:

• Co-produce special promotions you could not afford on your own.
• Have a contest with the prizes contributed by your partners. A very good example on the bakery located in Toronto who gave away a "Free" Powerball ticket with the purchase of $20.00. That was a brilliant marketing move. It gave their customer the convenience and they in turn made a huge profit. It was a win, win situation for both.

Online cross-promotion has the potential for a big marketing payoff because partners can successfully expand through one another's  client base.  Both you and your marketing partners can gain an inexpensive and credible introduction to more potential clients more effectively than with the traditonal lone-wolf methods of networking, advertising, or public relations.