Different uses for different grades or types of vanilla? Best sources for purchasing?

Unfortunately there is no standard grading procedure; different vendors use different criteria. Beans are generally graded for imperfections, size and moisture content. By imperfections, we're talking minor cosmetic differences, not something that should be an issue in the gift situation you describe. (Which, by the way, is not how vanilla extract should be treated. Exposure to light degrades the flavor and thus the reason it's sold in dark brown bottles.)

Grade A is best for splitting, scraping, and infusing in cream or other cooking purposes. Due to their lower moisture content, the lower the grade, the more economical they are but also the more difficult to work with. Any grade is fine for extract as moisture has virtually no effect on the outcome.

At home, I usually use grade A beans no matter the purpose. That way I can rotate them through, using the oldest for making extract.

You wouldn't have to move all the way to Fiji to start a vanilla business. The plants will grow in Hawai'i where people are apparently willing to pay $12 for a single bean.

Thank you all for the information! I get a sense from what I've read so far that grades refer to perfect vs imperfect beans, so if one is splitting/scraping then grade B is fine, and if one is say infusing whole beans in vodka in a clear glass jar for gifting then grade A is best.
It seems there is great variation in location, now I want to try the Costa Rican beans. Or move to Fiji and start a vanilla farm...

For our purposes, there are really only two types of vanilla: Planifolia (aka Bourbon aka Madagascar aka Mexican aka "Vanilla") and Tahitensis (aka Tahitian Vanilla). Only minor differences result from where they are grown and how they are processed but between the two types, Bourbon is the one everyone is familiar with, Tahitian is more delicate and floral. Experience will tell you where and when to use each type (or a mixture of the two).

Here's a good primer on the subject:

http://www.vanillareview.com/vanilla-information/

Tahitian vanilla beans have a lovely sweet flavor, but it's not as strong as the flavor of Mexican or Madagascar vanilla beans. I use Mexican vanilla beans during winter because the flavor is so robust: rich and earthy, with notes of tobacco. I would use the Mexican bean for a richer flavor in desserts during winter- bread pudding, ice cream, poached fruits, etc. The Madagascar vanilla bean is more delicate than the Mexican, with a sweet flavor reminiscent of cherries and licorice. Madagascar vanilla beans are often covered in a white, powdery substance called vanillin (which contributes to vanilla flavor and is associated with better grade vanilla beans). I like to use Madagascar vanilla beans in delicate desserts like panna cotta and puddings.
I buy vanilla beans from the Savory Spice Shop, which has brick and mortar stores owned locally as well as an online shop. Each type of vanilla bean has its own personality, and it's fun to try them and find your favorite. I don't worry too much about grades, just find a good supplier who carries quality product and let your palate be your guide.
In the summer of 2011 I spent a week on my blog experimenting with different types of vanilla beans for ice cream. You can read about it here:
http://www.ladomestique.com/2011/06/23/vanilla-bean-ice-cream-part-2/

I only buy my vanilla from Penzey's. I prefer Madagascar, I think it's the most aromatic.