All great options, no doubt, but if you are up against a deadline or can't travel to one of the clinics or Marfa, I suggest AceCFI.com. There isn't much glider-specific information, if any, but you will get a solid briefing on the FAA's Hot Sheet. If you go with an online course, don't discount the value of attending a clinic when possible.

I went with AceCFI.com two years ago because it's a lifetime renewal service once you sign up - i.e. your subsequent FCIRs with them are gratis.

As always, your mileage may vary.

Paul A.