Hey, I don't have to tell you where tribal tattoos come from, do I?
Many cultures around the world make it a standard practice to decorate their bodies with tattoos -- sometimes for religious significance, to promote cultural values or to note status within the group.
Why they're so appealing to us today is, I think, for a couple of reasons:
1 - The Look: While some die-hards are starting to complain that the popularity of tribal tattoos is getting boring, the reason they became so popular in the first place is simply because of how they look. I for one am still a fan.
2 - The Message: While tribal tattoos usually had very specific meanings to the actual tribes who used them, today the message conveyed by any particular tribal tattoo may vary from person to person. Personally, I always like to know where a particular tribal tattoo came from originally, and what it was supposed to signify. That way I can make a decision about whether I want to walk around with it for the rest of my life.
Choosing a tribal tattoo is no different, really, than choosing any other type of tattoo.
The design has to appeal to you. It has to "fit" with other tattoos you may already have. I don't mean fit spacewise, it should "fit in" with the overall thing you're going for.
Why not start taking a look at popular photo sharing sites -- like Flickr -- where thousands of people have uploaded pics of their own personal tribal tattoos.
It's a starting point, and that way at least you can get a sense of the style you're after.
To narrow it down from there, take a look at any of the dozens of sites that sell tattoo designs. If you can't find tribal art tattoos that meet your expectations there, chances are you never will.
Good luck and let me know how it goes.