For MIPSeb, there's Rough Cuts Linux, previously known as Hard Hat Linux, which is most of Red Hat Linux 5.1 ported for MIPSeb. You can get this at ftp://oss.sgi.com/pub/hardhat.
It is also bundled along with M68k, UltraSparc and PowerPC in a package called "Rough Cuts" pressed by Red Hat, and available wherever Red Hat products are sold. This is a very convenient way to get it without having to download 280MB. You can order Rough Cuts directly from Red Hat at http://www.redhat.com/product.phtml/RC1000.
As well, there's a distribution based on Red Hat 5.2 that's targeting the Cobalt Qubes; those binaries will work perfectly on other MIPSel architectures available at ftp://intel.cleveland.lug.net/pub/Mipsel. ftp://bolug.uni-bonn.de/mips has various rpm packages from Redhat 6.0 and 6.1.
A Debian port is underway. Current efforts are being bootstrapped using SGI/Linux as a base, and dpkg compiles natively with few changes. In addition to the SGI version, some interest has been shown in little endian platforms. Keep an eye on the Debian-MIPS Port page, http://www.debian.org/ports/mips/ for developments.
This distribution is for big-endian systems only so far. It's highly experimental, intended for developers' use in testing the latest versions of gcc, binutils, glibc, and the kernel. This is the only glibc 2.2 based distribution available for MIPS. You can always get the latest version of this distribution and accompanying release notes at ftp://oss.sgi.com/pub/linux/mips/mips-linux/simple. Also available is a cross-compiler system to aid in development.