I live in Baltimore so some sites are about the Orioles. I will add to this list and try to sort it into categories
Retrosheet
@Retrosheet
Retrosheet.org has information on games going back to 1871. If you know when you saw a game, you can find the box score.
Would it dong?
@would_it_dong
In how many parks would that home run have been a home run?
Orioles Player Development
@OsPlayerDev
Official Twitter account for the Orioles minor league system. Prospect rankings are here.
Baseball Fight Club
@mlb_fights
Fights at games
MiLB-Transactions
@tombaseball29
Minor league and major league transactions
MLB Foreign Substance Checks
@StickyCheck
Checks of players by umpires
Nathan Ruiz
@NathanSRuiz
Baltimore Sun Orioles beat writer
Stats By STATS
@StatsBySTATS
Stats for baseball and other sports
EddieMurray33.com
@EddieMurray_33
Hall of Fame player has a Twitter account and web site. He’s my favorite Orioles player.
MLB Draft League
@mlbdraftleague
New baseball league sponsored by MLB
The 1971 Orioles: Daily Report
@1970Orioles
Now tweeting the 1971 season when the Orioles lost the World Series to the Pirates but had four pitchers who won 20 games
Minor League Promos
@MiLBPromos
promotions and giveaways in the minor leagues
Kevin Brown
@kevinnbrown
Orioles broadcaster
InsideAccess1057
@IA1057TheFan
Baltimore sports radio show
The Baseball Newsletter
@bbletter
Daily newsletter
Baseball History Nut
@nut_history
Old baseball photos
The Athletic Baltimore
@TheAthleticBAL
sports coverage
John Means
@JMeans25
Orioles best pitcher
Reading Fightin Phils
@ReadingFightins
Phillies AA team
Delmarva Shorebirds
@shorebirds
Orioles minor league team
National Baseball Hall of Fame and Museum
@baseballhall
The Baseball HOF in Cooperstown
Mike Elias
@MElias
Orioles general manager
MASN
@masnsports
Orioles/Nationals TV network and a web site. Follow individual writers.
Anthony Santander
@roller_mvp
Orioles outfielder
Umpire Auditor
@UmpireAuditor
worst umpire calls
Grayson Rodriguez
@G_Rodriguez16
Top minor league Orioles pitching prospect
Baseball By The Book
@BaseballBookPod
podcast of interviews with authors of baseball books
Rich DubroffMLB
@RichDubroffMLB
covers the Orioles for Baltimorebasebll.com
Matt Kremnitzer
@mattkremnitzer
Orioles writer for Press Box Online
Cedric Mullins
@cedmull30
Orioles All-Star Outfielder
Gregg Olson
@GreggOlson30
Orioles closer in 1989/1990s
Baseball Prospectus
@baseballpro
Analysis
The Society for American Baseball Research (SABR)
@sabr
Baseball research
1960s Baseball
@Baseball1960s
Baseball history from the 1960s
O’s Stats & Facts
@BirdlandStats
Trivia and stats
Baltimore Negro Leagues
@BaltimoreEG
Elite Giant and Black Sox history
Jim Palmer
@Jim22Palmer
Hall of Fame Orioles pitcher
Ross Grimsley
@rgrimsley2
Orioles pitcher in the 1970s
Baseball Reference
@baseball_ref
Stats and history
Sporting News MLB
@sn_mlb
Baseball coverage
Eutaw Street Report
@EutawStReport
fan based Orioles site
MLB Communications
@MLB_PR
Major League Baseball Communications Department
The Major League Baseball Players Association (MLBPA)
@peloteros_MLB
The players association
Sad! 