Please do not hesitate to let me know if any of these blogs are no longer available or are inactive (no new posts for months.) Also, feel free to suggest new blogs for the list!
Thanks in part to the Sports Card Blogroll by bdj610 on Blogger for pointing me to many of these blogs!
A Pack to Be Named Later - http://apacktobenamedlater.blogspot.com/
A Penny Sleeve for Your Thoughts - http://pennysleevethoughts.blogspot.com/
Deals with a lot of older baseball cards, plus football cards, basketball cards, and non-sport cards.
Angels in Order - http://angelsinorder.blogspot.com/
Baseball Card Breakdown - http://baseballcardbreakdown.blogspot.com/
Baseball Cards Come to Life - http://borosny.blogspot.com
Baseball Dime Box - http://baseballdimebox.blogspot.com
Baseball Every Night - http://baseballeverynight.blogspot.com/
Beckett News - http://www.beckett.com/news/
Because it’s Beckett
Cards on Cards - http://cardsoncards.blogspot.com/
Collecting Cutch - http://collectingcutch.blogspot.com/
CrazieJoe’s Card Corner - http://craziejoescardcorner.blogspot.com/
Daily Autograph - http://www.dailyautograph.com/
Diamond Jesters - http://diamond-jesters.blogspot.com
Dodgers Blue Heaven - http://www.dodgersblueheaven.com/
Foul Bunt - http://foulbunt.blogspot.com
From a 1980’s Baseball Card Collector -
Johnny’s Trading Spot - http://johnnnystradingspot.blogspot.com/
Nachos Grande - http://fanofreds.blogspot.com/
A blog about baseball cards, the Cincinnati Reds, and Barry Larkin
Night Owl Cards - http://nightowlcards.blogspot.com/
Actually runs a lot of baseball card set blogs, too, like 1985 Topps.
Old Sports Cards - https://www.oldsportscards.com/
Also covers basketball & football
One Million Cubs Project - https://www.onemillioncubs.net/
An epic project in which Beau Thompson aims to collect 1,000,000 Chicago Cubs cards!
Pack War - http://packwar.blogspot.com/
SABR Baseball Cards - sabrbaseballcards.blog
Section 36 - http://section-36.blogspot.com/
Shoebox Legends - http://shoeboxlegends.blogspot.com/
Sport Card Collectors - http://sportcardcollectors.blogspot.com/
Sport Cards from the Dollar Store - http://buckstorecards.blogspot.com/
The Collective Mind - http://thecollectivemind.blogspot.com/
The Radicards Blog - http://www.radicards.com/
The Shlabotnik Report - https://shlabotnikreport.wordpress.com/
Writes about other sports cards and music, as well.
The Topps Archive - http://toppsarchives.blogspot.com/
This blog features all sorts of Topps cards, including non-sports oddities.
The Yount Collector - http://theyountcollector.blogspot.com/
Topps Blog - https://www.topps.com/Blog
Upper Deck Blog - http://upperdeckblog.com/
Because it’s Upper Deck
Wax Pack Gods - http://waxpackgods.com/
When Topps Had (Base)Balls - http://whentoppshadballs.blogspot.com/
Wrigley Wax - http://wrigleywax.blogspot.com/
Again, please leave a comment if you have an active baseball card blog you’d like to see added.