An Open Source Alternative
CiviCRM has a large community of users and developers that make this software possible. Depending on your situation that can be a plus or a minus.
It's been said before, but this software is not right for everyone. But it can be an affordable, flexible and robust solution- depending on your association's situation. Here are a few checkpoints:
Do you use Drupal CMS? If so, you're halfway home. Civi was built for Drupal and works best in that environment, though it now supports operating with Wordpress and Joomla. The integration of CiviCRM with a Drupal website makes membership forms and login functions much easier.
Do you have a Techie on staff? Not required (see below) but nice. Let your techie set up a sandbox and load some of your records. It will cost you nothing to actually see it work with your data.
Do you have international members? CiviCRM (and Drupal) can manage different languages pretty easily. Even multiple currencies can be used.
Is your budget tight? Civi costs nothing. That said, it won't do much unless you have a dedicated techie to configure it. The best approach is a hosted solution that specializes in Civi and understands it. Let them configure it and you can have a powerful system that costs thousands less each year than Microsoft-based systems.
If you said yes to any of those then you should at least take a look at Civi. It's definitely a different approach than most of the AMS on this site. But for some associations it's a great option.