Give this a try:
It's not a plugin... just a single tiddler that uses standard TWCore widgets.
To install it, just copy the tiddler into your document. It will automatically show checkboxes for all tags present in your document.
Select the combination of tags you want, and it will show you two results:
one for tiddlers matching ALL selected tags, and
one for tiddlers matching ANY (one or more) selected tags
enjoy,
-e
Eric Shulman
TiddlyTools.com: "Small Tools for Big Ideas!" (tm)