Listening over and over again to the set of records recorded by Tony Rice, J.D. Crowe, Doyle Lawson, etc., under the name 'The Bluegrass Album Band' was a big help to me when I was first learning to play bluegrass about 25 years ago. These still rank very high on my list of favorite bluegrass recordings.
Here is a link to 20 songs from the Bluegrass Album Band records. I hope you enjoy these. This is high-quality bluegrass well worth taking the time to listen to.
Finally, here is a list of other Bluegrass artists and bands besides Flatt & Scruggs and the Bluegrass Album Band to check out on youtube (or on any recordings that you can find for sale online or in local record stores) that I especially recommend for those who are new to Bluegrass:
The Stanley Brothers
J.D. Crowe & The New South
Ricky Skaggs and Kentucky Thunder
The Del McCoury Band
The Osborne Brothers
Jim & Jesse
Alison Krauss & Union Station
The Lynn Morris Band
Reno & Smiley
Almost all the songs on the beginner jam song lists have been recorded by one or more of these artists or bands, and there are many more songs recorded by these artists that are bluegrass standards and very jam friendly that are easy to find on online and in stores that have a decent bluegrass music section.