PracticePanther - PracticePanther offers CRM, invoicing, time tracking and communication solutions for law firms.
Leap - With Leap you find things based on your natural memory of that file.
MyCase - Practice More, Manage Less.
DEVONthink - DEVONtechnologies develops DEVONthink, DEVONagent, and other Mac and iOS apps for document and information management and web research.
Clio - Clio provides a full suite of web-based practice management tools targeted specifically at the administrative needs of sole practitioners and small firms.
Elyse - The free version allows up to 30 tags.