I found this idea in a budget decorating magazine... Didn't exactly fall within the budget, but that's my own fault. The key, I think, is to not fall in love with some fabulous and expensive ribbon, because you'll need a LOT of ribbon, so the cheaper you can get it, the better!! My ribbons look super shiny in my pictures, but they are actually a bit more colorful than they look here...
Lightweight fusible web, 3-inch strips x however long you want your curtain to be
Ribbons-- LOTS! (I used $$ Offray Lady Chiffon in a few colors & cheapy chiffon ribbon from Joann Fabric, both worked great)
Metal grommets and a grommet tool
Cut your ribbons into 78-inch pieces. You will need a lot, depending on how wide your ribbon is. Lay the ends of your ribbon onto the fusible web, one or a few at a time.
Use a warm iron to iron the ribbon onto the fusible web. Continue until you have 1-foot or so of all ribbons. Flip this over, so that the fusible web is on the top, then carefully fold the ribbons so that the fusible web is folded in half onto itself, with the ribbons on top.
Iron on top of the folded part, so that the web will fuse onto itself and the ribbons are folded. Continue these 2 steps until you have enough length for your curtain. Then you'll need to sew all of these strips together, end to end. Also sew the top and bottom of the strips for strength, because the fusible web is not that tough.
Once you sew these all together, you'll have a huge pile of ribbon and you might want to just give up!! But you're almost done!
You'll need a clear shower curtain to line the ribbon curtain, so lay all your ribbons out on the floor, so that the top strip that you sewed is flat. Lay your clear curtain on top, so you'll know where to put the grommets to hang your curtain. Mark each hole with a pencil or pen. Once you have it all marked, clip a little hole with a scissors on each mark, and use your grommet tool to put a grommet there.
Once your grommets are all in place, you're finally done!! I recommend hanging the ribbons on the outside of the tub when you're using the shower, and trying not to get them too wet too often, because it would be a shame to do all this work and have your ribbons get moldy. I think they look nice tucked into the tub, though, when the tub is dry (plus then my kitty doesn't play with them!)