I've posted these links in a couple of other threads. 

First one is an article about CMS:  Article

Second is a comparison chart from 2009, chart does not include all avail. programs.  This guy sends out a questionaire yearly,
does the chart off of info. he recieves:  Chart

I have no affiliation with this guy or anything, I find the chart helpful.  Especially if you are looking for certain tasks that a CMS
program can do for you.  For me it's offering a Denominational Version to help do yearly reports to the head office AND the payroll function that handles pastor's housing allowance.  For others it will be other qualities.

We use Servant Keeper and I love it.  The price is very reasonable and it doesn't have any ongoing fees.  I track EVERYTHING on it.  Things like small group participation, donation history, volunteer service record, special event participation.  I use their system for emailing.  I can send to our entire congregation (about 400 email addresses) all at once.  I can form groups based on any criteria in less than a minute.  I could not do what I do without it.