Linotype FontExplorer X for the Macintosh has been a free download for a long while. Like many other users, I switched to it awhile back and have been pleased with it, especially considering the price. LinoType has now revised FontExplorer X, giving it a new name (FontExplorer X Pro), adding a server version, offering support and documentation...and deciding to charge for the product. I can't blame them for charging. It's awfully hard to make money on a free product! Linotype is selling the "Pro" version for an introductory price of $39 through 2/28/2009.
You can still download the free version, but it will not be developed further, and at some point I assume an OS X system update will come along that will make this version no longer function properly.
Font management for the Macintosh has come a long way in the last couple of years, with capable font managers available from Linotype, Insider Software (FontAgent Pro 4) and Extensis (Suitcase Fusion 2). You really can't go wrong using the latest versions of any of these products. Each one has a slightly different focus and strengths and weaknesses. All three companies offer a server version to help manage fonts in workgroup settings also.