Basic contact management solutions can satisfy your needs as stated. I agree with Shipley that you first need a carefully documented set of "needs" so that you can properly assess the software available.
A sampling of factors to consider:
Who will use the system? How will they use it?
For each "use" of the system - What is the priority of that functionality relative to others? What is the business case behind having that functionality?
What will your future needs be? (as in, what might you ask of the software in 2 years, 5 years, etc)
What other software in the office should it work with? Its likely you'll want to integrate with or encompass your donor database as both perform the same essential function ~keeping track of important information related to your constituency. Perhaps in the future you'll want integration with the website and broadcast email.
After an assessment you'll have clear functionality you can take to vendors to find the simplest and cheapest solution.