Post links to English-language image boards here. There are about FIVE BILLION, but here's a couple of obvious ones:

http://www.2chan.net/ - Futaba Channel, the original.
http://www.nijiura.com/ - Nijiura, with the OS-tan board.
http://www.nijiura.net/ - Nijiura, adult version.

http://f6.aaa.livedoor.jp/~poppo/

http://akitakejyo.s31.xrea.com/

http://kisyapoppo.web.poporo.net/