For now, I am using printable iron-ons to make the labels, although I may go the Spoonflower route once I decide on a final layout for the labels (there's a lot of wasted space at the moment).
To make your own, design them on the computer, then print them out using the instructions that came with the iron-ons, which probably includes printing them backwards. They are currently 4x3, so I could fit six on a page. Here are five of them, cut apart:
Then trim around them to get rid of most of the white space:
And iron on!
I turned under the edges and hand-stitched to the quilts, but you could also sew them on by machine before quilting, which is what I think I'll be doing in the future.
I always knew I was supposed to make labels, but it was just always too much trouble--but these look good enough for me to want to put them on quilts!