In no order:
- Wireless internet: The ability to take the internet to class, to fields, and anywhere else you may like is pretty damn cool.
- The internet itself: no explanation necessary.
- The light bulb: my default answer. Think about how different things would be if still by candlelight.
- Soap: just to appease the medical world.
- Fire: Technically a discovery, and not an invention. But because it led to cooked food, it gets a mention.
- Birth Control: Idea courtesy of a friend, when he was asked the question. Self explanatory, really.
- The ball: Perhaps also a discovery, but I'm going to go with the first manufactured ball, with the intent to play sports. Fantasy geeks everywhere thank you.
This list is far from comprehensive- just starting the debate.
Addendum: I've been told I forgot the printing press, and the combustion engine. Both good.