There are several sources that would be very good to include in an intro page. IWTG is good and does not require an account but stops at the minimum needed to start playing with a full deck, i.e., ko.
For people new to the site, a reference to Senseis Library World Wide Rank Comparison table is useful to have http://senseis.xmp.net/?RankWorldwideComparison. Also useful for players here who decide to go to other venues.
321Go http://321go.org/home/ covers the basics but has more advanced material too; making a free account opens up access to a lot of resources (basic tactics, problems, a youth website, etc.) Language coverage is parochial compared to IWTG, just English, French, German, Dutch, Portuguese, Swedish.
IGS also has a nice introduction to Go http://www.pandanet.co.jp/English/introduction_of_go/ that goes beyond the basics IWTG offers and no account is needed.
In addition to IWTG, I refer new players to Senseis Library http://senseis.xmp.net as a reference. I think it’s worth directing attention to Basic Living and Dead Shapes and Good and Bad Shape. They can find just about anything else starting there.
Everyone gets told to do Go problems, there are probably lots of sources but GoProblems.com http://goproblems.com is old and has the 30k to 6d time trials.
Another thing that’s nice to know about is Go Proverbs. I guess there are online sources, I have a well worn copy of The Nihon Ki-in Handbook of Proverbs trans. & ed. by Max Golem.
One online source for Joseki is http://eidogo.com. It includes Joseki Tutor: Kogo’s Joseki Dictionary and Kombilo / Pro Game Database (which lets you select a series of opening moves and see games where that configuration occured.)
References to the various major Go organizations are a valuable resource. Six of them cover a lot of the world and the IGF lists all.
American Go Association http://www.usgo.org
European Go Federation http://www.eurogofed.org
Nihon Ki-in http://www.nihonkiin.or.jp/english/
Korean Baduk Association http://english.baduk.or.kr (NK has one. So what.)
China WeiQi Association http://www.weiqi.net (Taipei and HK have ones too but that might start a war.)
Australian Go Association http://www.australiango.asn.au
International Go Federation http://www.intergofed.org lists 76 organizations in Africa, Americas, Asia, Europe, Oceania