I've been using Aweber for about 18 months now & find it easy to use, has some good standard templates & you can import your own logo, pictures etc. If you can use the basic editors on this forum, you can use Aweber & make some great looking emails.
The only problem with it, is that you can't import your own current list. But with a clever IT guy, there are ways round this!!
It definitely has the double opt in you are looking for & since we started using them, our bounce rate has drastically reduced - something you need to take into account with any email service you select. It's no good having a "cheap" service, if they haven't done the work to make sure they are not blacklisted by a lot of ISP's.
I think I pay about US$50 a quarter. You can get more info at
www.aweber.com
Hope this helps.
Paul