Inspiration is often an elusive beast. I can sometimes go for months without doing very much tie-dye, just because I don't feel inspired by anything new to try out. And then there are other times when I'll be tying and/or dyeing every day or two, because I just can't wait to see the next set of results.
I get a lot of inspiration from other people, as many artists do. My friend with the tie-dyed couch has been a great inspiration lately, partly because of what he has been trying out himself with his own tie-dye (he's big on marbles), and partly because of his sheer "no matter what, it's gonna turn out great!" joie-de-tie-dye. I wish he could bottle that stuff!
Another friend gets inspiration for her oil paintings, and moral support to just keep working at it, from groups of other artists online (see her blog for more inspiration). The Internet has really made it easier to find support and inspiration from far-flung places--you don't have to host a salon in Paris anymore.
When you need an inspirational boost, books and videos can really be useful. Both the video "The Art of Tie-Dye" with Michael Fowler, and the video "Learn How to Tie Dye: Complete 3 Volume Set" with Tom and Martine, show some really inspirational pieces, even if you don't want to just follow their "cookbook" steps. The "Tie Dye, Back By Popular Demand" book by Virginia Gleser is an inspirational starting point too. Dharma provides even more inspiration on their website with their "Featured Artists" section.
But for complete "this is why I do it" inspiration, kids are the best. My daughters enjoy wearing tie-dye, and are quite happy to suggest what they'd like to add to their wardrobes! One of them likes to dye her own, and both of them are always happy to "adopt" shirts, sheets and other tie-dyed treasures that emerge from my work area in the garage.
First graders, Girl Scout troops, and other groups of kids are also good. The abundant energy and the wild abandon with which kids dye their pieces just charges the entire atmosphere. It's hard not to absorb their enthusiasm and want to dive in to do a few more pieces of my own.
While it's a lot of work, some of the volunteers (including me) who do the annual first-grade tie-dye project with the local school almost fight over getting to take the shirts home to wash en masse. Getting to look at all those wild shirts at once really gets the creative juices going.
But that's enough for now. I've got to go get my next batch in the wash...