I'm with everyone else-Forever 21, Target and I love Banana Republic's jewelry too.
My absolute favorite place though, is actually in Naples, Florida and it is called "The Best of Everything". The atmosphere is kind of Gatlinburg meets Las Vegas meets Grandma (they have tons of sparkly crap and such) and they blare this weird kind of elevator music and they have lots of fake flowers...but...they have some great costume jewelry for cheap. If you are ever in the area, check it out (but I warned you-you have to dig around a bit to get through the cheeze!)...
I dont really buy cheapie jewelry very often- but, when I do, I look for a sale first, and then the best quality I can get for under 20.00 per pair. I dont like to buy expensive, because I only where earrings, and no matter how hard I try, I end up losing them. I dont think of buying earrings until I have lost nearly every pair( such as now) and then I will go out and buy a whole bunch, and then Im good again for 6 monthes. It may sound weird, but buying jewelry causes me a little stress-even though I dont spend alot on each individual purchase. Probably because I know that I will be losing them soon. But, also because I have problems creatively when it comes to accesorizing. When I do buy, I tend to buy mainly at Macys. You can get a really nice, well made pair on sale for 15.00 or so. I have bought jewelry at Claires, NY and Co., and Target- but- I have bad luck with them not holding up to wear- so dont buy there anymore.