I took a huge bag of coins I'd been collecting for about 4 years now into the supermarket and pumped 'em into Coinstar.
The grand total was $182.13. Not too shabby, considering it didn't include all the quarters that went to coin-op laundry back in Michigan!
But here's the kicker... if you take your profits in the form of a gift card instead of cash, you get to keep 100% of the amount you put in (only some machines support gift cards, so you should do an advanced search on coinstar.com first before running for the nearest supermarket).
So now I've got a $182.13 Starbucks card.