What is Bitcoin?
Bitcoin is the first digital currency that is completely distributed. The network is made up of users like yourself so no bank or payment processor is required between you and whoever you're trading with. This decentralization is the basis for Bitcoin's security and freedom.
Your Bitcoins can be accessed from anywhere with an Internet connection. Anybody can start mining, buying, selling or accepting Bitcoins regardless of their location.
No small print
If you have Bitcoins, you can send them to anyone else with a Bitcoin address. There are no limits, no special rules to follow or forms to fill out.
More complex types of transactions can be built on top of Bitcoin as well, but sometimes you just want to send money from A to B without worrying about limits and policies.
Very low fees
Currently you can send Bitcoin transactions for free. However, a fee on the order of 1 bitcent will eventually be necessary for your transaction to be processed more quickly. Miners compete on fees, which ensures that they will always stay low in the long run. More on transaction fees (Bitcoin Wiki)
Own your money!
You don't have to be a criminal to wake up one day and find your account has been frozen. Rules vary from place to place, but in most jurisdictions accounts may be frozen by credit card collection agencies, by a spouse filing for divorce, by mistake or for terms of service violations.
In contrast, Bitcoins are like cash - seizing them requires access to your private keys, which could be placed on a USB stick, thereby enjoying the full legal and practical protections of physical property.