DownThemAll! 1.0 Firefox extension is an easy way to try out
Metalinks
        aria2 0.13 with even more features...
        Speed Download 5 for Mac
        Ubuntu Brainstorm: Make ISOs availiable as a .metalink
        debindex searches Debian archives
        KGet 2 is updated in KDE 4.0.1
        TheWorld Browser with Metalink support
...

        DownThemAll! 1.0 (Firefox extension) is out! This is the easiest way
to try out Metalink!

"the dTa Team is proud to introduce you to DownThemAll! 1.0. This is
the best DownThemAll! version ever.

It's faster, due to an improved chunks management and a better queue
book-keeping. It's more stable, thanks to his new download core and to
a smarter error handling. It offers new interesting features, like
support of metalink, checksums and LinkFingerprints."

http://www.downthemall.net/
...
        aria2 0.13 (Unix/Win), the high speed command line download utility
with Metalink support, is out! Try out aria2fe, a friendly GUI front
end, while you're at it.

http://aria2.sourceforge.net/
http://www.aria2fe.com/
...
        Speed Download 5.0. (Mac), the slickest download manager, is out.
Still with handy Metalink support.

http://www.yazsoft.com/
...
        Ubuntu Brainstorm: Make ISOs availiable as a .metalink

        We'd like to see this happen :) Wouldn't you?

http://brainstorm.ubuntu.com/idea/811/
...
        debindex is a Debian archive URL index that creates Metalinks for
downloads.

http://www.debindex.net/
...
        KGet 2, part of KDE 4.0.1, supports Metalink. Check the release
announcements for ways to try it out!
        "KGet - KDE's Download Manager" mentions the new features, including
Metalink.

http://www.kde.org/
http://francis.giannaros.org/blog/2008/02/02/kget-kdes-download-manager/
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        TheWorld Browser (Windows) is the first web browser with native
Metalink support. It's got a built in download manager and looks
great!

http://www.ioage.com/en/index.htm
...