Here is a simple and cheap way to get your arduino power.
This instructable only use "three things" and can be finished ~1 minute :-
1. power connector (for Arduino Uno, it is 2.1mm power connector)
2. "2-pins" terminal block
Although I want to write something, but it seems u can understand by viewing the photo.
1. unscrew the power connector and bend it (as photo shown).
2. shorten 1 pin of the terminal block
3. solder them
U can now easily power your arduino...
Step 1: About the Plastic Part of the Power Connector.
From this instructable, the plastic part of the power connector was left.
This plastic can be used as 5mm LED cap which shown on the photo.
Have a look :