I would like to send transactional Salesforce email via ExactTarget

Simple example, process :
1. New customer (using personal accounts)
2. Welcome email using email field

What is the best approach/practice to send those type of emails via ExactTarget?

Thanks

We are in need of a solution to send our transactional emails from our force.com application. Examples include when an item has been entered, a payment made, etc. We can no longer use the core SFDC functionality as we exceed the limits. 

Does anyone have any recommendations on the best solution to use that:

1. Allows fields to be pulled from Standard and Custom Objects and incorporated in the emails?
2. Can be tracked in Salesforce
3. Fairly easy to create / include templates
4. Can leverage workflow / triggers to send the emails

This isn't an email marketing solution but a solution that would enable us to send emails to customers as different actions occur. For example, something like Mandrill or SendGrid.

Thanks for any recommendations you may have!