If you are a Windows 8 or Windows Phone user, MiraCast is the way to go. (Some support Android - The windows one has the Android logo on it's page and says Android 4.2.1 or higher)
Unlike some of the other solutions like ChromeCast or Apple TV, it acts the same as attaching a WIRED 2nd monitor to your laptop or tablet - No "Casting" or special apps...
You can use DUPLICATE mode and everything on your device shows up on the projector or TV
Or
You can use EXTEND mode and your projector or TV acts like a dual monitor setup (Have your browser or Excel open on your tablet or laptop while running Netflix on the projector or TV)
It does Audio and Video:
Here are links to the 3 I have in order of my preference:
Microsoft - $59.95 - Pros: Direct from Microsoft, Size, USB Powered, Best I've used! Cons: Only available for pre order from Microsoft and Best Buy (I got mine as a giveaway at an event)
Actiontec ScreenBeam Pro - $69.99 - Pros: Many cool options in the firmware Cons: Wal Wart required for power.
NetGear PTV3000 - $49.99 - Pros: Price and USB Powered Cons: None
These things are not only awesome for home use (I have them on most TV's I own), but even better in conference rooms at the office - Especially the Exec conference rooms where audio and video cables on the conference room tables are "unsightly" :)