The usual disclaimers apply. This is not a complete list (it's not even my complete list) and many informative accounts are not listed here. And of course I am not endorsing every tweet by every account here. However, these accounts will help keep you current and, in some cases, present you with interesting/challenging analysis. You will likely see many of them retweeted (sometimes frequently) by me @BlogsofWar as I continue to track this story closely.
@20committee - John Schindler. Professor, Naval War College; Chair, PfP CT Working Group; Senior Fellow, Boston University; former NSA & NAVSECGRU - talking intel & security
@2kdei - Kristina Dei. OSINT, PR, IR, #eDiplomacy, #ForeignPolicy, Polyglot Director: Go Global Media.
@AFP - Agence France-Presse. News - and the stories behind the news - from AFP's reporters around the world.
@AmbassadorPower - Samantha Power. United States Ambassador to the United Nations.
@andrewsweiss - Andrew S. Weiss. Vice President for Studies, Carnegie Endowment. Russia and Eurasia Program. NBC News Analyst.
@BBCDanielS - Daniel Sandford. I'm the Moscow Correspondent for BBC News.
@BBCSteveR - Steve Rosenberg. Moscow Correspondent for BBC News.
@b_judah - Ben Judah. Writer, Wonk. Author of Fragile Empire: How Russia Fell In And Out Of Love With Vladimir Putin. Often heard talking to Monocle 24 radio.
@BSBonner - Brian Bonner. Kyiv Post chief editor and regional coordinator of Objective investigative journalism project.
@carlbildt - Carl Bildt. Foreign Minister of Sweden since 2006.
@CoalsonR - Robert Coalson. Radio Free Europe/Radio Liberty correspondent covering Russia, Ukraine, Belarus, Moldova, Balkans, South Caucasus.
@CrimeaEU - Crimean Tatar Parliment Representation to the EU.
@CSISRussia - The Russia and Eurasia Program at CSIS provides research, analysis, assessment, and recommendations regarding all the regions of the former Soviet Union.
@DmitriTrenin - Dmitri Trenin. Carnegie Moscow Center’s Director. Editor in chief of #EurasiaOutlook, the blog of @CarnegieRussia.
@europatweets - Europatweets - What is Europe doing - Aggregating most of Twitter accounts concerning Eu affairs
@ForeignCorresp - Christian Fraser. BBC Paris Correspondent - formerly Rome/Cairo/MiddleEast. Tweets on all things Europe.
@FHeisbourg - François Heisbourg. Chairman/Président IISS, GCSP conseiller spécial/special adviser FRS.
@GeoffPyatt - Geoffrey R. Pyatt, is the current United States Ambassador to Ukraine.
@GermanyDiplo - News from the German Foreign Office.
@Interpreter_Mag - Interpreter Magazine is a Russian-to-English translation journal, with news analysis and commentary.
@jamesmatesitv - James Mates. Europe Editor, ITV News.
@jancienski - Jan Cienski. Financial Times Warsaw correspondent.
@jason_corcoran - Jason Corcoran. Bloomberg News Irish journo in Moscow.
@JohnKerry - John Kerry. 68th U.S. Secretary of State.
@joshuafoust - Joshua Foust. Communications officer at the Eurasia Foundation.
@juliaioffe - Julia Loffe. Senior editor at The New Republic.
@JustHovensGreve - Just Hovens Greve. Freelance journalist and student.
@Kasparov63 - Garry Kasparov. Chairman of the Human Rights Foundation (@HRF). Author, speaker, 13th World Chess Champion.
@Kateryna_Kruk - Kateryna Kruk is a civil activist and political scientist based in Kiev.
@KevinRothrock - Kevin Rothrock - Russia analyst. Global Voices @runetecho Project Editor. UConn PoliSci PhD student.
@KimberlyMarten - Kimberly Marten. Ann Whitney Olin Professor of Political Science at Barnard College, Columbia University; international security specialist.
@KremlinRussia_E - President of Russia. Official Kremlin news.
@KrsBauer - Christophe Bauer. News producer at France 24 in Paris. Conflicted Franco-Haitian-Washingtonian. Politics/history nerd.
@KyivPost - The Kyiv Post is Ukraine’s leading English-language newspaper.
@lauraphylmills - Laura Mills. Moscow correspondent Associated Press.
@LawDavF - Sir Lawrence David Freedman. Professor of War Studies King's College London.
@lrozen - Laura Rozen. Reporting on Washington, foreign policy & Middle East.
@Lucian_Kim - Lucian Kim. Swiss-Korean American journalist on Crimea rehab in Kiev.
@MarkAdomanis - Mark Adomanis. Consultant by day, Russia watcher, blogger, and commentator by night.
@MarquardtA - Alexander Marquardt. ABC News Middle East Correspondent.
@MaximEristavi - Maxim Eristavi. Freelance foreign correspondent covering Ukraine. ex-@RFERL & @VoiceofRussia.
@michaeldweiss - Michael Weiss.? NOW Lebanon columnist, Foreign Policy columnist, Editor-in-Chief of http://interpretermag.com.
@mike_giglio - Mike Giglio. Mideast Correspondent for BuzzFeed.
@myroslavapetsa - Myroslava Petsa. Foreign Correspondent at @5channel, ex-@chastime. @NaUKMA alumni.
@NSCPress - This account is run by President Obama's National Security Council (NSC).
@NATOpress - Oana Lungescu. Official Twitter account of the NATO Spokesperson, Oana Lungescu. Ex BBC Europe correspondent.
@OdessaBlogger - Nikolai Holmov. Brit permanently in Ukraine.
@OSCE - The Organization for Security and Co-operation in Europe is the world's largest regional security organization.
@PaulSonne - Paul Sonne. Moscow correspondent for The Wall Street Journal. Currently in #Ukraine.
@pwaldieGLOBE - Paul Waldie. European Bureau Chief, Globe and Mail.
@RFERL - Radio Free Europe/Radio Liberty has 700 journalists in 21 countries broadcasting in 28 languages.
@rm867 - Rod McLeod is a regional security/crisis director, US multi-national, operating in Europe, the Middle East & Africa.
@RNicholasBurns - Nicholas Burns. Harvard Kennedy School Professor and former American Diplomat.
@RolandOliphant - Roland Oliphant. Moscow correspondent for @telegraph.
@shaunwalker7 - Shaun Walker. Moscow Correspondent of the Guardian.
@shustry - Simon Shuster. Reporter in Moscow for TIME.
@SimonSmithFCO - Simon Smith. British Ambassador to Ukraine.
@SlawomirDebski - Slawomir Debski. Director of @CPRDiP. Former head of the Polish Institute of International Affairs.
@steven_pifer - Steven Pifer. Brookings scholar focusing on arms control, Russia and Ukraine. Retired career diplomat.
@strobetalbott - Strobe Talbott. President, Brookings Institution.
@tanais_ua - Natalia S. Researcher (Ukraine, Eastern Europe, civil society, EU foreign policy).
@TheWarRoom_Tom - Tom Nichols. Professor, Naval War College. Former US Senate aide. Adjunct @HarvardEXT. Politics, foreign policy, Russia.
@tkesho3 - Eka Tkeshelashvili. Lawyer, President of Georgian Institute for Strategic Studies. Former Vice Prime Minister, Minister of Reintegration, Foreign Affairs and Justice.
@youbsanctioned - Sam Cutler. Policy Adviser @ Ferrari & Associates, P.C. Tweeting on sanctions, AML/CFT, IOC, and the day's int'l crisis.
@YuliaSkyNews - Yulia Bragina. Russia and CIS producer for Sky News.
@zbig - Zbigniew Brzezinski. National Security Adviser to President Carter. Counselor and Trustee @CSIS. Research Professor at SAIS.