You can got to common bookmarking tools (like del.icio.us) and try to find your topics. Most of the tools offer a list of related tags.

A list of bookmarking tools can be found here:

http://itredux.com/blog/2007/01/15/bookmarks-roundup/

Moreover http://quintura.com/ is a tag-cloud search engine. Have a look at common tags/words "close" to your topic.

Regarding with or w/o underscore, I have no definite answer. The issue is that some tools cannot work with spaces, thus they are substituted by underscores.

Same issue as for file/folder names and spaces regarding URL-autoformat in tools like MS Outlook.