GeoKit is a new Rails plugin developed by Bill Eisenhauer and Andre Lewis that provides several powerful geocoding related features:

• Location and distance finders for ActveRecord models.
• Distance calculations between any points on the earth.
• Multiple provider geocoding (Google, Yahoo, Geocoder.us/ca) with fallback support.
• IP-based location lookup.

The ActiveRecord finders are really slick, check out this example:

Location.find(:all, :origin => 'Irving, TX', :conditions => ["distance < ? and city = ?", 5, 'Coppell'])

The developers have blogged about their new creation here and here.