Its probably not the sources.list file.
Failed to fetch http://ftp.de.debian.org/pub/debian/...y-i386/Release Cannot initiate the connection to 8080:80 (0.0.31.144). - connect (22 Invalid argument)
The bold indicates that it is your proxy info that is causing the problem. You might have the format messed up.
I use on the command line:
"export http_proxy=http://userasswd@proxyort"
"export http_proxy=http://james01:[email protected]:80"
"export ftp_proxy=http://james01:[email protected]:80"

Then apt-get & aptitude & even synaptic work just fine.