You can requests tutorials here if there isn't an existing tutorial you would like to see.
Useful tools:
GMOD12 :\
Smartsnap http://www.garrysmod.org/downloads/?a=view&id=121887 (http://www.garrysmod.org/downloads/?a=view&id=121887)
No-Collide all Multi V2 http://www.garrysmod.org/downloads/?a=view&id=110922 (http://www.garrysmod.org/downloads/?a=view&id=110922)
Weight tool 1.4 http://www.garrysmod.org/downloads/?a=view&id=19331 (http://www.garrysmod.org/downloads/?a=view&id=19331)
Stacker tool http://www.garrysmod.org/downloads/?a=view&id=45634 (http://www.garrysmod.org/downloads/?a=view&id=45634)
Advanced Duplicator V2 http://facepunch.com/showthread.php?t=1136597 (http://facepunch.com/showthread.php?t=1136597)
Multi-Parent http://www.garrysmod.org/downloads/?a=view&id=77936 (http://www.garrysmod.org/downloads/?a=view&id=77936)
Multi-Unparent http://www.garrysmod.org/downloads/?a=view&id=122581 (http://www.garrysmod.org/downloads/?a=view&id=122581)
Wenlis' Tools http://www.garrysmod.org/downloads/?a=view&id=119510 (http://www.garrysmod.org/downloads/?a=view&id=119510)
http://sourceforge.net/userapps/mediawiki/wenli/index.php?title=Main_Page (http://sourceforge.net/userapps/mediawiki/wenli/index.php?title=Main_Page)
Specialist tools:
Wiremod svn: http://www.wiremod.com/forum/installation-malfunctions-support/4-wiremod-svn-guide.html (http://www.wiremod.com/forum/installation-malfunctions-support/4-wiremod-svn-guide.html)
GMOD 12 :\
Fin tool 2.3 http://www.garrysmod.org/downloads/?a=view&id=30333 (http://www.garrysmod.org/downloads/?a=view&id=30333)
MakeSpherical 2.1 http://www.garrysmod.org/downloads/?a=view&id=131011 (http://www.garrysmod.org/downloads/?a=view&id=131011)
Existing tutorials:
Sparrow's fin tutorial, this can give you a basic understanding of fin tool plus a way to control it. (http://forum.randomgs.com/index.php/topic,13228.0.html)
Mr White's independent suspension tutorial plus steering, no wire required. (http://forum.randomgs.com/index.php/topic,13229.0.html)