Email Stripper helps with this and more!
http://www.papercut.biz/emailStripper.htm

eCleaner e-mail cleaner is better than Email Stripper IMHO.

eCleaner v2.01 is a freeware application that helps you clean the "> or  |" or
any other mark used that accumulate after an e-mail message has been forwarded
many times. It will also get rid of all addresses in the header as well as clean
up HTML garbage. Once it is cleaned up simply copy again and paste into a new
message. You can also print it from the application if needed.  It should work
for any version of Windows (95/98/Me/NT/2000).

Also, if you are using Outlook 2000 an add in module has been made to
incorporate the eCleaner function directly into the e-mail toolbar.
(Not available for other email programs)

http://ecleaner.tripod.com/
http://ecleaner.tripod.com/clean202.zip