Is there any chance you can be proactive and suggest that a certain day of the week (or part of day) be kept open for meetings?  I know this is a tough sell, but if these meetings are critical it may be a proactive way to get evey one to the meetings.

    There is a wonderful (and easy to read) book called "Death by Meeting".  Is the meeting really necessary or could a document suffice to get the information to the team?  Also are there any ways of combining meetings?  If not everyone needs to be in all of the meeting there could be staggered times for staff members to come in and out - this also helps to keep meeting on track and on schedule because the next group will be coming.

    I agree outlook is a lifeline IF everyone uses their calendar! Is it possible to make any of the meetings reoccuring - even monthly?

    My last suggestion is does everyone have to be present or can they call into the meeting?  Granted this is not the best option but at least they will have heard the meeting if maybe not participated in it.