Recommended: Affordable under-sink Culligan models US-EZ-3, and US-EZ-4.
Link to Amazon - Culligan EZ-3
Link to Amazon - Culligan EZ-4
A fantastic water filter "Technology Explainer" is at EWG.org
Link to EWG.org -water filter technology
Link to EWG.org -water filter buying guide
Link to EWG.org - step-by-step water filter Guide