Check for dents very carefully before you leave. Gas her up at the end. Look for free upgrades. Enterprise may be worth checking. They pick you up and drop you off.
Definitely the two biggest "scams" of the rental car industry is offering insurance and offering to fill the gas tank. What they don't tell you is that most of the time your personal auto insurance also covers rentals, so you're just wasting your money there. Also, pass on the deal where they will fill the gas tank for you for a nominal fee. First, the price per gallon that they charge will always be more than if you just find the gas station yourself (if they charge per gallon), and second, (if they charge a flat fee), that fee will usually be more than if you just filled it up yourself.
The one I like the most, however, is don't accept their offer to upgrade your vehicle if they are going to charge you for doing so. The reason for this is chances are the reason why they are offering this is because they are out of the size you had reserved in the first place and are trying to stick you with the costs of the upgrade. If you stick to your guns chances are you get the upgrade anyway and don't have to pay a dime for it. That's what happened to me last week - I had a midsize vehicle reserved, and by the time all was said and done I was driving a Ford Mustang all week and I didn't have to pay a cent extra for it.