Spotlight so much as one of the index plugins (mdimporters)

This probably isn't Spotlight so much as one of the index plugins (mdimporters). 

Spotlight itself is very robust, however, all it takes is a single bad indexing plugin. 

MDS, basically, identifies a file type and loads in a list of plugins that are registered for that file type and executes a routine in the plugin to grab the metadata. 

If the plugin is improperly written, it can go haywire. 

What was the last application that you installed prior to it going crazy? 

Perhaps one of the last 2-3... Failing that, you can wipeout the metadata database for a Volume like so 

(from Terminal.app)

: sudo mdutil -E /Volumes/your_volume_here ... 

or '/' in place of '/Volumes/...' for the local disk. 

You can turn off metadata indexing for a volume entirely like so

: sudo mdutil -i off /Volumes/your_volume_here 

You may also want to see what index plugins are being used

: sudo lsof | grep mdimporter ... 

which might help you understand what's being used to index, and this

: sudo lsof | grep mdworker 

... will tell you what worker threads are running and the files they have open (some of which will be the files they are indexing).