The best of the rest
Other Apple applications offer the odd useful 'tweakable' setting. Here are our favourites:
11. Activate iCal's Debug menu
defaults write com.apple.iCal IncludeDebugMenu 1
Although not as feature-rich as the old Safari Debug menu, iCal's equivalent provides a 'new window' item, enabling you to show multiple calendar views simultaneously.
12. Force plain text in Mail
defaults write com.apple.mail PreferPlainText -boolean true
If you're fed up with HTML emails, the above command over-rides such things and takes you on a trip back to the 1990s. (If after applying this you can't access attachments in an HTML email, either use Quick Look to access them, or use View > Message > Next Alternative or Command+Option+].)
13. Unify Finder views
defaults write com.apple.finder FXListViewStripes -boolean false
Only Finder's list view has stripes. Remove them using the above rule and in Terminal type 'killall Finder' and then Return to restart Finder. Use 'true' rather than 'false' to reverse.
STRIPE-FREE: A quick trip to Terminal can remove the stripes from Finder's list view
14. Make Help Viewer less hateful
defaults write com.apple.helpviewer NormalWindow -boolean yes
It'd take more than the above command to make us love Help Viewer, but this at least stops it from floating above other apps, laughing maniacally as it blocks everything else from view.