I've used the pigma micron pens - they come in fine line and brush tips and in lots of colors. The gel pens work really nice, too. I experimented a while back with the gel pen - wrote on a scrap and then wshed, scrubbed, etc. to see what would happen - and nothing happened at all! And they come in lots of colors. I truly would not use Sharpie pens though as they are not made for fabrics - and here's my reason: I have a white cotton shirt that I have used for NASCAR autographs. All the guys use Sharpies - and autographs now have yellow halos around the writing. Doesn't look like bleeding, just this halo that doesn't look very nice.
You can also print nice labels from your computer printer - some printer ink is better than others for staying power - and I probably would heat-set just in case (do that for the pigma pens, too). The scrapbook stores havesome nice permanent pens you might want to check out. Manufacturers websites might give more info on the ink and how it works with fabrics.
Hope this helps - I tend to get a bit wordy!!
Sandy in Mooresville, NC (visiting in Kirkland, WA at the moment)