Poparide (previously named HitchPlanet) is a Vancouver-based Uber-like service that connects you with people who are making the drive and have an extra seat. It is an excellent, inexpensive, fast, and convenient option to get from Squamish to Whistler and back.
The only question is whether you'll be lucky enough to find a driver who's got a seat available for the time your looking for. Typically you'll find a few rides available every day, and the number is increasing as Pop Rideshare continues to grow in popularity.
Rides typically cost $7 dollars each way and the drivers are often flexible on pickup and drop-off locations.
The Squamish Connector
Running daily service between Vancouver and Squamish, and Squamish and Whistler, check out their website for details and schedules: Squamish Connector.
The Shred Shuttle
Starting the 2017/18 ski season, The Shred Shuttle will offer rides between Squamish and Whistler, departing Squamish in the morning and returning from Whistler in the afternoon (check here for up-to-date schedules). It costs $20 return, or, $12 one way.
Seats are limited and sell out fast quickly, especially on the weekends. The biggest plus? They pick up from the Squamish Adventure Inn's front door, right to either Whistler Creekside or Whistler Village - and back.
Other
This site appears to be now up and running https://www.squamishrides.ca/ Check it out!
Whistle Rides offers lifts between Whistler and Squamish: https://www.whistle.ca/
More Ways To Get From Squamish To Whistler and Back?
If you know of any, please do share in the comments. We'd love to hear about them!