jQuery sliders:

• Build a Content Slider with jQuery :: Brenelz’s Web Development Tips
• Easy Slider 1.5 – The Easiest jQuery Plugin For Sliding Images and Content | Css Globe

jQuery tooltips:

• jQuery TOOLS / Tooltip – Tooltips done right
• qTip – The jQuery tooltip plugin

Usability testing:

• Low cost usability testing – UserTesting.com
• userfly — Web usability testing made easy
• Chalkmark – User Interface Testing
• Loop11 (via Smithy)

Misc:

• 10 Ways to Instantly Increase Your jQuery Performance – Nettuts+
• 247 web usability guidelines