How and where to find them is another matter (did you see How to find joint venture marketing partners?).  But what qualities will you search for in your ideal fusion marketing partners?

Bits and pieces of advice can be found in some of the articles linked from the page titled Joint venturing...  How others see it.  Here's a list to make the basics easier to keep in mind...
  

Look for a business that...

• Has a large customer base, or reaches a large audience in some other way
    

• Keeps in frequent contact with his customer base, or advertises regularly
    

• Treats her customers very well
    

• Has a loyal following that trusts in the business' reputation and expertise
    

• Has products or services (or just information) that complement your own offering
    

• Has a clientele that is willing to spend money on your products or services 

Or are you looking for an individual? - who...

• Represents the voice of integrity to your target market

  
A little more about the ideal fusion marketing partner...

First of all, the ideal is good, certainly... but may not be required!  You may prefer to test the waters, for instance, with someone whose clientele is smaller.  You may find a great match in a business that only sends out a couple of mailings a year to its customers. ...Don't let the "ideal" stand in your way!

With that said, though, there are good reasons to look for the ideal.  (And to be delighted when you find it!)

We'll delve further into that list from above...
  

• The ideal fusion marketing partner...  Has a large customer base, and/or reaches a large audience in some other way

The larger, the better... if it's targeted for your purposes.  (If only partially targeted, that's okay - but keep in mind that it's not so good a deal for you. ...You might not offer as much in return - monetary compensation for an endorsement, for instance.)

Websites and e-zines can be highly targeted - or not.  The same goes for print advertising or direct mail promotions.  Again, a less accurate target isn't necessarily bad for you - it just isn't as good as ideal.

But let's not overlook all the other possible means of reaching people!...  Radio shows/ads.  Newspaper columns.  Billings.  Theatre program printing.  Over-the-counter sales bagging.  Well-publicized stunts. ...Put your thinking cap on!  Why shouldn't you team up with whoever might help to publicize your business creatively and inexpensively?

Let's also not overlook the impact of exclusivity... where "large" isn't necessarily the most operative attribute of a group.  "Best targeted" might be much more important in the long run.
   

• The ideal fusion marketing partner...  Keeps in frequent contact with his customer base, or advertises regularly

Advertising, in the traditional sense, is often more a branding than a persuading force...  It generally takes people a number of times viewing the same ad before they respond to it by doing something.  One reason is that they want to know that the business is established... and you want to know that!  A repeated ad infers that the ad - and the business - is successful.  If you're attracted to a potential fusion marketing partner by an ad... look for it in succession.

Then, in general...  The more regularly a business keeps in touch with its clientele, the more chances it has to impress them and secure their loyalty.  Then, the more chances you might have to tap into that resource.  This assumes, of course, that the business' contacts are welcomed by its clientele...
   

• The ideal fusion marketing partner...  Treats her customers very well

Repetition may be good for the business, but what's good the for customer has to be a top priority - that's what cements customer loyalty.

A business treats customers well by making their needs come first in all things...  They ensure good customer service.  They select products and services that their target market wants and needs.  They stick to the "you" in their advertising instead of the "me".  They don't "sell" - they offer and inform.

A business might also treat some of it's customers especially well...  In giving sales to "preferred customers" (which could be simply repeat customers, or frequently-repeating, or the biggest spenders).  In setting up a "V.I.P. club" for some.  In hosting parties, giving bonuses, sending out birthday cards, etc.

These set-apart customers can be excellent targets for joint venture deals...  Ask your prospective fusion marketing partners whether such opportunities exist in their businesses.
  

• The ideal fusion marketing partner...  Is a business that has a loyal following that trusts in the business' reputation and expertise  OR...

• An individual who represents the voice of integrity to your target market

For a business, customer loyalty derives from the characteristics mentioned above.  It might also be brand-related, if that applies - i.e., a reputation can be built by word of mouth, not just via a customer's direct experience.  But the bottom line is - has loyalty been built?

Many businesses use endorsements by "celebrities" to boost their image...  hence the "individual" option mentioned.  Such an endorsement aids in the trust extended to the business as well.

I put celebrity in quotes, though, because the person doesn't have to be famous, only respected in some way and perceived as having integrity.  And of course you'd want a bona fide user of your product, not just a "hired gun" - your promotion has to be believable.  "Always highlight the benefits," seasoned JV marketer Jay Abraham stresses...

So your celeb can be anyone whose opinion would be highly regarded under the circumstances. ...You don't have to know who the president of a major corporation is to be impressed that she's an avid user of a particular product because it helps her in her business practices.  Her status, and/or her relationship to the product, lend distinction to it, even if her name and face aren't well-known.

We all know that celebrities can be bought...  Many people, though, are willing to endorse products or services that they actually do have experience with, and partiality for. ...And their sincerity may have a far greater impact on potential new customers than the "sanctioning" (presumed to be for money, even if not) of a sports star!
    

• The ideal fusion marketing partner...  Has products or services (or just information) that complement your own offering

This is part of the targeting that you need to do...  What would make sense for your offering?

This gives great scope for the imagination!  For a list of brainstorming ideas, see the page titled But how to come up with a great joint venture marketing concept?  Suffice it to say...  Keep open to all the possibilities around you.

...Sell a golf seminar video? - Team up with golf-related websites, or with sellers of golf tees.  With golf pros and course clubhouses.  With a famous golf resort.  With manufacturers of golf clothing and shoes.  With high school and college golf instructors.  With vendors of Father's Day gifts.  With well-known female golf pros.  With photographers who videotape golfers' swings for them to review.  With sellers of golfing books.  With golf course realtors. ...Etcetera etcetera etcetera!  In fact, what about with sellers of other, complementary golf seminar videos?...

Many people are surprised to learn that very successful joint ventures are engaged in by people whose businesses compete with each other.  Their businesses may compete, but the individual products that they promote for each other don't. ...And they certainly know that cross-promotions are reaching super-targeted customers!
 

• The ideal fusion marketing partner...  Has a clientele that is willing to spend money on your products or services 

This is likely to mean for you, "Go where the money is"...  Look for JV partners whose customer base is proven to spend the right kind of money on the kind of product or service.  Sometimes this isn't immediately apparent...  To illustrate:  "Don't try to sell furniture to college students (sell it to their parents).  Don't try to sell computers to secretaries (approach the company that hires them)." - Mike Enlow