这是台湾ntu的源，教育网比较快
deb http://ubuntu.csie.ntu.edu.tw/ubuntu/ dapper main restricted universe multiverse
deb http://ubuntu.csie.ntu.edu.tw/ubuntu/ dapper-updates main restricted universe multiverse
deb http://ubuntu.csie.ntu.edu.tw/ubuntu/ dapper-backports main restricted universe multiverse
deb http://ubuntu.csie.ntu.edu.tw/ubuntu/ dapper-security main restricted universe multiverse
deb http://ubuntu.csie.ntu.edu.tw/ubuntu/ dapper-proposed main multiverse restricted universe
cn99的源，电信比较快。
deb http://ubuntu.cn99.com/ubuntu/ dapper main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ dapper-updates main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ dapper-security main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ dapper-backports main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu-cn/ dapper main restricted universe multiverse
上海交大的
deb http://ftp.sjtu.edu.cn/ubuntu/ dapper main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ dapper-backports main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ dapper-proposed main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ dapper-security main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ dapper-updates main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu-cn/ dapper bleeding main multiverse restricted universe
官方指定的
deb http://archive.ubuntu.com/ubuntu/ dapper main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ dapper-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ dapper-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ dapper-backports main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu-cn/ dapper main restricted universe multiverse