Podcasts
Joe Bussard’s Country Classics
Sound Beat
Radiola!
Gramophoney Baloney
Scratchy Grooves
Venerable Music Radio
Radio Dismuke
Bear Family Radio
Hot Jazz Saturday Night
Dick Spottswood’s Bluegrass Country
Backroads and Banjos (with Art Rosenbaum)
The Shellac Stack (with Bryan Wright)
Sinners’ Crossroad (with Kevin Nutt)
The Sound of 78s
Antique Phonograph Music Program
Down Home Radio Show
Thomas Edison's Attic

Resissue Record Labels & Archives
Library of Congress National Jukebox [free]
UC Santa Barbara Cylinder Preservation and Digitization Project [free]
Belfer Audio Archive Cylinders Digital Connection [free]
78Records [free]
honkingduck 78s [free]
Archive.org 78 collection [free]
Ragtime Dorian Henry [free]
Phonomono78s [free]
Dailymotion User KSPM0220s [free]
Cliff Bolling's "CDBPDX" [free]
Popular Jazz Archive [free]
Document Records
Dust to Digital
Smithsonian Folkways
Yazoo Records
Juneberry 78s
Old Hat Records 
Archeophone Records
JSP Records
Bear Family Records
County Records
Old Homestead Records
Take Two Records
TinFoil.com
Herwin Records

Blogs & Informational Web Sites
Old Time Party
Mainspring Press Blog
Excavated Shellac (International)
ShellacHead (International)
VJM Articles
Don't Stay Up Too Late - See especially "100 great records..." series
BluesWorld.com
Hell Hound on my Trail
Ted Staunton's 78rpm Label Gallery
Hillbilly Music
Lonesome Lefty's Scratchy Attic
Old Time Music Home Page
Folk Archivist
Heypally's 78rpms

Record Auctions
Nauck's Records
Green River Records
Hawthorn's Antique Audio
VJM's Vintage Jazz and Blues
Venerable Music Auctions

Discographies & Collectors' Resources
Online Discographical Project (78s)
Allen Koenigsberg's Phonobooks.com
Encyclopedic Discography of Victor Recordings (EDVR) at UC Santa Barbara
Stefan Wirz - A collector's site with many blues discographies
Survey of Leading Acoustic-Era Recording Artists
Tim Gracyk's Collectors' Info
Little Wonder Records / Bubble Books
Index of Record Research Magazine

Sheet Music Collections
UCLA Sheet Music Consortium (Searches Multiple Collections)
Library of Congress Historic Sheet Music Collection, 1800-1922 (and finding aid (PDF))
Baylor University Spencer Collection of American Popular Sheet Music
MSU Charles Templeton Digital Sheet Music Collection
Johns Hopkins University Levy Sheet Music Collection
National Library of Australia - Sheet Music
University of Tennessee Sheet Music Collection

Organizations
Association for Recorded Sound Collections - see ARSClist
National Audio-Visual Conservation Center
78 Informational Listserv
78 Commercial Listserv   
Association for Cultural Equity - Alan Lomax Archive
Library of Congress' American Folklife Center
Virtual Gramophone - Library and Archives Canada
AHRC Research Centre for the History and Analysis of Recorded Music (CHARM)
FirstSounds.org
UNC Southern Folklife Collection
Indiana University Media Preservation Initiative
Audiovisual Preservation Solutions
Cool Conservation

Technical Info & Reports
LC/CLIR National Recording Preservation Plan (PDF)