Information

Email Newsletters
These are the best in the industry (IMHO).
Skift

Travel Market Report

TravelPulse

Travel Professional News

Travel Weekly

Research Firms
Forrester

Phocuswright

Advertising & Customer Experience Agencies
These are the ones that I have worked with. 
Aveus

bvk

Capsule

MMGY Global

Ogg Marketing Group

Twitter Handles
This is by no means is a complete list but, it is a start.
@AAA_Travel
@aioutlet
@anthonyqbowen
@ASTAAgents
@avoyatravel
@awtravelweekly
@Bourdain
@bizarrefoods
@cntraveller
@CPMichelle
@cruisecritic
@CruisePlan
@Cruisitude
@DondraCel
@elliotdotorg
@EPIC_DMC
@fodorstravel
@forrester
@foxworldtravel
@funjetvacations
@gogobot
@IATA
@JetSetExtra
@KateRiceNYC
@KHMTravel
@LMErecruiters
@lonelyplanet
@LuxeTiffany
@MMGYglobal
@MorrisMurdock
@myhostagency
@NACTA4U
@nexionllc
@nytimestravel
@phocuswright
@richardbranson
@RobertCole
@RTDenton
@samanthabrown
@skift
@TandTNews
@thetraveleditor
@tipsytraveler
@tnooz
@Travel_Zap
@TravelAuthority
@travelchannel
@travelgov
@TravelHaus
@TRAVELinstitute
@TravelLeaderRDU
@TravelLeaders
@TravelLeisure
@travelmassive

@TravelProComm
@TravProNews
@TravelPulse
@TRAVELSAVERS_US
@travelwriting
@Travel_Zap
@traviskatz
@TrvlMillennials
@twtravelnews
@TzellTravel
@USTOA
@usatodaytravel
@vcom1
@VWT_Travel
@wendyperrin
@zagatravel