I get asked about CRM often. Personally, I use an Access database and Outlook. That will need to change soon. It is clunky.
I really liked Landslide, but now that J2 (the efax people)bought them it is now Campaigner CRM. EH. I haven't tried it but the name sounds like it is tied to email campaigns, right?
The big boy on the block is of course Salesforce.com. If you use Broadsoft based phone service, Salesforce Premium hooks into the system for click dialing. Expensive though.
The other whale is Microsoft Dynamics CRM. If you aren't using Hosted Exchange and Sharepoint, this might be cumbersome. It is designed to work with the entire, latest-and-greatest Microsoft suite of products. If you are reselling MS, you should be using their system, too. Although I have partners that sell white-label and retail MS, I don't use it.
If you use Google Apps -- maybe I should say, if your clients use Google Apps, then Insightly is worth a look. It is the most popular CRM for G-Apps.
Zoho has been around a while and has an office/email suite too. Zoho CRM integrates with G-Apps too.
SugarCRM comes 2 ways: open source so you can play with it and hosted so you can just use it as the tool that it is. It is clunky, but for you folks that have to have control, there you go.
For you 37Signals fans that use Basecamp project management software, there is Highrise. They also offer a free plan (2 users, no files, 250 contacts) and a solo plan (1 user, 5 GB file storage, unlimited deals, 20k contacts, $29/month).
Some people I know are using Batchbook. "Batchbook is a simple tool to help you build meaningful relationships with your best customers." It's an Andrew Jackson every month.
"VMware Zimbra is an enterprise-class email, calendar and collaboration solution, built for the cloud, both public and private. With a redesigned browser-based interface, Zimbra offers the most innovative messaging experience available today, connecting end users to the information and activity in their personal clouds." You can run it on your equipment or you can get it white-labeled by VAR Dynamics. The CRM is not sold stand-alone; you have to take the whole suite.
There are plenty of others but those are the ones I can think of.