Other OC based forums are
www.overclockers.com.au - Its much the same as oc.com and OCforums. I never post there as i dont have time but from all accounts its a very good place.
www.extremeoverclocking.com - You could check out this place. It semes ok but again i dont post there.
www.overclockersclub.com - ditto
The best casemodding site is
www.bit-tech.net but its not a 'overclocking' forum. Never the less its a fun place to hang out. Expecialy if your from the UK (which i see your not but we welcome all)
TBH other than OCAU and OC.com theres not relly any other top notch general overclocking sites around. Thats why i dont want to see OC.com go down the pan!
Theres alot of [H]ard ocps out there im afrade
Edit: heres a few more i pulled from my bookmark list
http://www.ocaddict.com/
http://www.octools.com/
http://www.ocinside.de
And there just the ones that start with OC. you will have to make you own mind uo if they are any good.