For feature addons - there's a couple of places.
The biggest is www.ThreadsDev.com
Also www.ThreadsAddons.com
(Both are my sites <img src="https://www.ubbcentral.com/boards/images/graemlins/wink.gif" alt="" /> )

Also if you can dream it... i can usually do it - contact me at www.joshuapettit.com/contact to discuss custom coding.

For graphics, I know you know about JC, so I'll list some alternatives.
Generally - when I have a need - I use Jason Parker
http://www.sorael.com/

He's working with me on *another* software project, but has also done several UBB.Threads themes for me and my clients.

Nikos from ThreadsDev is also quite talented.
http://ib-designs.net/
and www.niden.net

There are a few other graphic designers looking for work here:
http://www.threadsdev.com/forum/showflat.php/Cat/0/Number/64905
I'll add Lane to this list:
http://www.threadsdev.com/forum/showprofile.php?Cat=0&User=10835
He's done some great UBB.Threads designs.

Coders looking for work here:
http://www.threadsdev.com/forum/showflat.php/Cat/0/Number/59143

Joshua Pettit
Web Developer
www.ThreadsDev.net | www.JoshuaPettit.com