Amazon Simple Email Service
$0.10 per 1,000 emails sent. 65K free emails per month if you are hosted on EC2.
Disadvantage: You can only sent from @your-domain.extn, if you have a SAS application and need to sent from some other email address, you need domain added to SES and verified.
https://aws.amazon.com/ses/pricing/
ElasticEmail
Free plan allows you to send 150K emails per month.
Disadvantage: All outgoing email must include physical address.
MailGun
First 10K emails for Free every month. Pay as you go pricing. After 10K free email, you will be charged $0.00050 per email.
MailJet
Free account allow you to send 6,000/- email per month. Monthly plan start at $7.49 per month for 30k emails.
SparkPost
50K Emails for $9 per month. If you are on AWS, you can get it cheaper from marketplace.
SendGrid
40K email per month for $9.95 per month.