IATS is a subsidiary of Ticketmaster that offers an excellent way for non-profits in Canada to get transaction processor services - you don't even need a merchant account, and it's relatively inexpensive. It's a step up from a service like 'canadahelps' because you can integrate it into your site and get the donor data into a CRM automatically, and can also be used for e-commerce (in theory).
Up until now though, there was no plug-in for their service with CiviCRM. I had begun a project to write one about a year ago, and after a long hiatus, just finished one. If you're using CiviCRM 1.7 or above and have an IATS service in Canada, please try it here:
http://homeofficekernel.blogspot.com/2007/12/iats-and-civicrm.html
If you're in the US, and want to help out, either take a look at the code and enable the US section, or bug me and I'll send you a US-enabled version for testing. I've been reluctant to have it work out of the box because I don't know anything about US credit card requirements/law, and it seems to be different that Canada (e.g., different required fields).

Comments
Drupal integration with IATS
Do you know if anyone is working on a facility to use IATS from Drupal Ecommerce or Ubercart?
also looking for this
Would love to get a client that has just moved to Drupal 6 nicely integrated with IATS. Has anyone done this yet?
thanks!
iats & drupal 6
if you're talking about IATS w/ CiviCRM 2.1, then it's really no different than IATS w/ earlier CiviCRM versions. The only difference vis-a-vis other transaction services is that the configuration in the db isn't pre-configured, but you'll get all the info you need at the link above.
If you're asking about IATS and e-commerce, then you're in the wrong group.