I've been using online meeting coordination solutions for quite a while now and find them to be incredibly helpful for sending invitations, managing RSVP lists and keeping guests updated until the actual event. Here's a few of the ones I've used that you may want to try.
The newest one on my radar is Coordinatr. If you need an easy way to send out instant notices via email about an event that allow recipients to RSVP immediately, this could be your new favorite site.
Normally, I use Evite for my events where RSVP management is useful. I even used Evite for my wedding invitations and figured friends and family would understand based on the fact that I live and breathe the Internet. Coordinatr is a much more pared down invitation service so simplicity and speed are the benefits of using this site over Evite.
For more formal community building, where you'd like to turn online meetings and communications into offline meetings, try MeetUp. MeetUp is free for people looking for real-world meetings with like-minded people but if you are a meeting organizer, you have to pay a fee. I was paying approximately $79 per quarter to organize a group called Motherhood Later Than Sooner, for moms over 40 with kids under 5.
MeetUp provides you with online communication tools for your group members, from message boards to an email list to a calendaring system for your real-world events. For example, Motherhood Later members organize not only a monthly MeetUp at Marty's New York Bagel on Dimond but also music gatherings for moms and their kids and a reading time at the library.
For truly quick coordinating of meetings or even conference calls where you are wrangling the schedules of several to many people, try the no-frills site Doodle. With Doodle, all you have to do is enter your event. Then add date and time options. Then you can email people to invite them to check in their available dates and times.
Doodle provides you with two links: one to administer your doodle page and one to send to others to access to respond to your scheduling query. After everyone checks their availabilities, you can access your admin page where you can see where everyone's schedules mesh to book the call, meeting or event.
All of the tools I've mentioned are free to use other than MeetUp for organizers. Both Coordinatr and Doodle do not require that you become a member while the others do to get the most use out of their services.
When you need to organize meetings and events, nothing beats Web applications although when it comes to the personal touch, there is still no Web site that can match the hand-written note.