• HSQLDB: 100% Java Database
• MySQL: Open souce Database
• MySQL Connector/J: Official MySQL Java driver
• Jexcel: Java excel driver
• BrowserLauncher2: Browser launcher java library
• Launch4j: Jar wrapper to create windows native exe's
• Log4j: Java logging library
• Dotuseful: Java library with Swing Tree classes extension
• Tablelayout: TableLayout is a powerful and free layout manager
• HttpClient: HTTP java library
• Retroweaver: Java bytecode weaver
• Java Native Access (JNA): Dynamically access native libraries.
• MediaInfoLib: Media file parser
• JasperReports: Report creation utility
• IzPack: IzPack Java Installer
• Lobo: Java Web Browser: Pure Java browser
• Cobra Toolkit: Cobra: Java HTML Renderer & Parser
• The Castor Project: Data binding framework for Java

Here are some nice Look & Feels for Java:

• Skinlf: Skin Look & Feel
• JTatto: JTattoo Look & Feel
• Substance: Substance Look & Feel
• Office LaF: Office Look & Feel
• JGoodies LaF: JGoodies Look & Feel
• Kunstoff laf: Kunstoff Look & Feel

Javootoo - Look & Feels collection site.