I have a website on Cashel / Cashell, focusing mainly on Ireland, and mainly on Co.Kerry and Co.Tipperary, but including lots of other places. Please have a look and send any additions or corrections:
http://computing.dcu.ie/~humphrys/FamTree/Cashel/contents.ht...
http://computing.dcu.ie/~humphrys/FamTree/Cashel/
http://computing.dcu.ie/~humphrys/FamTree/Cashel/misc.html
The main Cashel(l) family of Co.Kerry descend from Anglo-Irish gentry and ultimately from nobility and royalty, as you can see at the above site, so this is pretty much the most interesting surname in my family tree. Let me know if you can add anything!
Dr. Mark Humphrys
Lecturer
School of Computing
Dublin City University
http://computing.dcu.ie/~humphrys/
http://computing.dcu.ie/~humphrys/FamTree/