What we use: Your Mailinglist Provider. They have a free version for smaller mailinglists: you can send 1000 emails for free every month. Let's say that you send an email twice in a month, with 450 recipients: that's 900 emails sent in a month. It's free, easy, reliable and fast. The free account is also very good if you want to test the software and compare it with some other services. Visit Your Mailinglist Provider for more info about the different accounts. Also read our YMLP review.
Get Response is another quality service. The pricing of this service is a bit higher: 10 dollars per month for a list of 1000 subscribers.
Finally, there's Aweber. You can test their service out during 1 month (they only ask 1 dollar for this). After that it's about 19 dollars per month (up to 500 subscribers). There's no limit on the amout of emails that you are sending. If you've got more subscribers, then you'll pay extra. Up to 2500 subscribers it's about 30 dollars extra per month.
All of these services are continually working to offer new options to their users!
Look at this comparison: Aweber vs GetResponse and YMLP.