I have a love/hate relationship with costume jewelry. It needs to be a specific combination of inexpensive and amazing to pique my interest.
This ring did it for me.
Costing about $6 (my mom does sell Avon), this ring looks like it's worth many, many, many times more. Big and flashy without being cheesy, and I love that the bow is assymetrical (one loop is void of rhinestones). I layered this on top of another ring, but it looks much better on its own. Avon claims this will adjust to your fit, but if you have smaller hands (like I do), your best bet is to put it on an index or middle finger.
Full retail price is $19.99.
This piece is a must-have - girly, more sparkle than other rings I have which were MUCH more expensive, and Avon jewelry is of really good quality.