Solution 1:

I don't think there's a plugin for Deluge, but flexget is an RSS torrent downloader that is very easy to configure, extremely flexible and has tight integration to Deluge. I use flexget+Deluge and it works fine.

Take a look at this for details on Deluge integration

Solution 2:

I don't think Deluge has an rss feed downloader, but qBitTorrent does and is an excellent client.

qbittorrent Install qbittorrent

See Comparison of BitTorrent clients

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Solution 3:

KTorrent has rss feed and is an excellent client. If you are using Gnome, then it will install "some" dependencies too, because is a KDE application.

ktorrent Install ktorrent

See Comparison of BitTorrent clients

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Solution 4:

A little late to the discussion, but...

Deluge has an RSS plugin called YaRSS2. Vuze can handle RSS, too, but it's written in java and so it doesn't integrate well with GNOME. The slightly beefier Miro can, as well, but it either has a bug or plays nanny about what torrents you can download. If you want to use Transmission, there's an insanely complicated-looking setup described here on Ubuntu Forums