I usally don't respond to these things but I will put in my 2cents for what it's worth because bluegrass in one of my passions.
If you are looking for knowlege in the roots of the music and how the sound was formed over it's first few decades go to 'the father' and 'the king'. Bill Monroe and Jimmy Martin should be at the top of the list. Any of the first generation players are worthy. As far as recordings, the Bear Family has a great catalog of box sets of a lot of the classics. More that you can probably stand. Flatt and Scruggs alone has 3 box sets that are 4, 5 and 6 discs each. You will find Monroe, F&S, Martin, Osbornes, Country Gents, Mac Wiseman, etc. They do a great job and the quality is as good as you can find out there...not cheap though.
As far as modern day, I will have to agree with Cruz123 in that most of the things on the radio would not be considered bluegrass. The new term is 'contemporary bluegrass'. It is kind of the same thing that happened to classic country music. I am by no means saying that there is anything bad about it, it's just not bluegrass. The albums I tell people to listen too, if they are unfamiliar with the genre, is the 'Bluegrass Album Band'. Any and all of the 6 volumes. Tony Rice, Doyle Lawson, JD Crowe, Bobby Hicks, Jerry Douglas, Todd Phillips and one even has Vasser Clemens for the twin fiddles. All covers of great traditional tunes played they way they were ment too. Killer from start to finish.
For those that are keeping that tradition sound alive today... here are some of my favs. Jame King Band, Michael Clevland, Del McCoury, Mark Pruitt's new band 'Balsam Range', Brian Sutton, Blue Highway, Doc Watson, JD Crowe and the New South, Doyle Lawson...to name a few.
The internet radio thing is also a great tool. I will ad a plug for our local radio station WNCW. You can stream it. Saturdays they play 8 hours of bluegrass music, straight from the heartland.
Hope this hels you on your quest.
Hope this helps.
