Drinks are just so much better with lime juice that came from limes rather than a container with all the requisite processing.
Squeeze some damn limes! You can freeze lime juice for later use and it works fine.
Freeze it in an ice cube tray so you can pull out descrete units!
That's it.
I use one cup of sugar and one cup of water in a Pyrex measuring cup, and nuke it in the microwave for two minutes, or until it just starts boiling. The last of the sugar at the bottom will disolve with stirring.
You can make it in a saucepan too. It's not rocket surgery.
I make it in advance and store it in the fridge in a bottle with a pouring spout. Wicked convenient.