Here's a simple Applescript program to create The Hit List tasks from Mail.app mail messages. It will create them in the Hit List Inbox with a start date and notes taken from the body of the mail message.

 
tell application "Mail"
	try
		set theSelection to the selection
		if the length of theSelection is less than 1 then error "One or more messages must be selected."
		repeat with theMessage in theSelection
			my importMessage(theMessage)
		end repeat
	end try
end tell
 
on importMessage(theMessage)
	tell application "Mail"
		try
			set theSubject to subject of theMessage
			set theDate to date received of theMessage
			set messageURL to "Task created from mail message:%3c" & (message id of theMessage) & "%3e"
			set theBody to messageURL & return & return & the content of theMessage
			tell application "The Hit List"
				tell inbox to make new task with properties {title:theSubject, notes:theBody, start date:theDate}
			end tell
		end try
	end tell
end importMessage
 

Copy the above text or download the script file

I use it by setting up a keystroke using Spark that only applies in Mail.app. It makes it trivially easy to create tasks from mail messages.

If you haven't seen The Hit List yet I highly recommend it. Not only does it work well but it's even beautiful to look at.

Updated: Used Andy Kim's version with the single addition of the start date.