I did the Litmus Survey 2018 for the first time. One of the questions was about ESP in use. Although not every ESP is included (Freshmail was missing!) it is still a great list of available ESPs on the market.
ActiveCampaign
Act-On
Adestra
Adobe Campaign
Adobe Marketo
Adobe Magento
AWeber
Aurea (includes Lyris)
Benchmark Email
Black Baud (includes Convia & Luminate Online)
Blue State Digital
Campaign Monitor
Campaign Monitor Emma
Campaign Monitor Delivra
Campaigner
Cheetah Digital (formerly CheetahMail)
Clang
ClickDimensons
Constant Contact
Cordial
dotMailer
eBay Enterprise
Emarsys
emfluence
Epsilon
ExpertSender
Freshmail
GetResponse
HubSpot
IBM Watson Marketing (formerly Silverpop)
IBM Unica
iContact
iModules
Infusionsoft
iPost
Iterable
Listrak
Mad Mimi
MailChimp
Mailgun by Rackspace
Mailigen
Mailjet
Mapp (includes Blue Hornet)
Marketing Service Company
Maropost
Microsoft Dynamics
NationBuilder
NewZapp
Optivo
Oracle Bronto
Oracle Dyn
Oracle Eloqua
Oracle NetSuite
Oracle Responsys
Oracle Siebel
PostUp (formerly Pulseconnect)
Pure360
Real Magnet
Sailthru
Salesforce Core
Salesforce Marketing Cloud (formerly ExactTarget)
Salesforce Pardot
Salsa
SAP
Selligent (formerly StrongView)
SendinBlue
Sendy
SmartFocus (formerly EmailVision)
SparkPost
SharpSpring
Streamsend
Tikit EMS
Twilio (includes SendGrid)
Vertical Response
Vision6
WhatCounts
Yes Marketing (formerly Yesmail)
Zeta Global (formerly Acxiom)