I use a combination of Unbounce (to host my launch page) and MailChimp (to handle emails). Unbounce has a page builder that is really easy to use - you can have a page setup and accepting email addresses in 10 minutes. I integrate Unbounce with MailChimp, so when someone enters their email address it automatically gets sent to MailChimp. MailChimp is great for sending emails to lists of people. They also handle setting things up correctly so your emails arrive in your subscriber's inbox instead of their spam folders.
Both services have a free tier which should work for the early stages of your venture.
If you want to send one email in isolation there are loads of tools available, some mentioned above. However, if you want to sedn emails in a structured way, the start of a communications journey then consder the bigger picture.
As well as regular series of emails things could be triggered, for instance if somebody asks for a trial or demo.
So having more logic and functions could be relevant. Also if somebody repsonds to an email, via a landing page they are a "lead"?? So where do you put the lead? When the lead becomes a customer what do you do?
Tools like LAMP-360.com allow you to send emails but as part of the bigger picture of demand and lead generation and building relationships and ultimately customers.
I work for LAMP whcih provides functionality of CRM, EMail marketing, social puboishing , content management, landing pages at a value price that a start up can afford and can use....as we are a start-up ourselves I thought I would post on here. There is a free version to do the basics and then you can upgrade to do more....