On a quest for the perfect knowledge base

I've been on a quest for some time now.

I'm seeking the perfect notepad type application to act as a PORTABLE knowledge base - All too often i'll see a link or find a fix for something and want to record the information somewhere for future usage. I'm looking for a tool that is:

• Portable (i.e. can run from a USB key)
• Doesn't need to be installed
• Can be split into categories
• Is searchable
• Can hold a large amount of data.

I did try tiddlywiki but after adding a couple of articles the .htm file it generates got too large and it became very cumbersome to use so the search goes on...