We accidentally missed the release of Uncomplex’s Mailplane 2.5 a few weeks ago, which gives the Gmail-specific email client support for full-screen mode in Mac OS X 10.7 Lion, along with support for the new Preview Pane feature from Gmail Labs. Otherwise, the Mailplane 2.5 release fixed bugs relating to Boomerang and Rapportive, addressed some Lion-specific bugs, and automatically adds the Evernote toolbar button when the Evernote application is installed. The just-released Mailplane 2.5.1 adds a Window > Enter Full Screen menu item and keyboard shortcut for Lion users, removes the conflicting keyboard shortcut from Mail > Forward, and fixes some problems with sending messages, uploading attachments, and two-finger swipes in Lion. ($24.95 new, free update, 22.5 MB)
Mac OS X Zip Expanding Utility
Firefox (and possibly other applications) may ask you what you want to do with .zip archives that you download from the Internet. If you want to expand them with Mac OS X (rather than StuffIt Expander), you may be unsure of which application actually does the job. You're looking for Archive Utility (in Leopard and later) or BOMArchiveHelper (in Tiger). In either case, the application is stored in Hard Drive/System/Library/Core Services/. Don't move it from there, though, or you'll confuse matters.