Adobe InDesign Plug-ins
Sure, they have fonts. But they also have plug-ins. Font-related, of course. FontGazer is for previewing and purchasing fonts from right within your InDesign document. Then there's a Photoshop extension — fonts.com Web Fonts extension — for preview/purchase of fonts from within Photoshop. Both are for CS5 and up.
Em Software InData
Plug-ins include InData, InCatalog, and InFlow for managing database and spreadsheet data in Adobe InDesign. They also do QuarkXPress XTensions.
Cropster ID adds many cropmark options. ProScale ID] is a resizing tool. Other InDesign plug-ins handle slugs and document splitting.
In addition to tutorials and industry news they provide reviews of plug-ins and other add-ons for Adobe InDesign.
Learn about the latest plug-ins, including lots of free plug-ins and scripts for Adobe InDesign.
WoodWing Smart Plug-ins
Smart Styles and Smart Layout add flexibility and features for users doing complex layouts such as magazines, newspapers, catalogs, and more. Free demos available for these and other InDesign plug-ins.