oh and I know pencils work well on mini blinds and such, but I'd like a marker because the dark black is much more readable when you're sorting out an order of 12 different heirloom tomatoes to ship out.

Paint pens. You can find them in craft stores or the craft department of your local x-mart for $3 or $4. The first labels I made with these are now 6 or 7 years old and are still perfectly legible. They come in all colors, but I'll warn you that some of the colors will fade - they don't disappear, but I know that pink will fade to white. Still legible, just not pink anymore! I use black for most things; white is nice for writing on plastic pots. And I find the medium tip to be the best for visibility from a distance so I don't have to stoop over to read the tags.