The Arnamagnaean Institute, Copenhagen
Concordance to proverbs and proverbial material in the sagas - Richard Harris's incomplete but already very useful conspectus of proverbial material in Old Norse (currently mainly restricted to the Sagas of Icelanders).
Eddic and Skaldic Poetry - An interesting miscellany of texts and commentary on various eddic and skaldic poems by an Icelander whose identity is not made clear. Includes an incomplete digitization of Finnur Jónsson's Lexicon Poeticum.
EGIL: Electronic Gateway for Icelandic Literature - A comprehensive set of links to resources for the study of Old Norse, Icelandic literature, and the Viking Age, hosted by the University of Nottingham.
The Fornaldarsögur Noršurlanda - A digitized version of Gušni Jónsson and Bjarni Vilhjįlmsson“s three-volume popular edition (Modern Icelandic orthography) of the 'Sagas of Antiquity', created by Zoe Borovsky at the University of Oregon.
Fritzner's Ordbog Online - The standard dictionary of Old Norse (for anybody who reads Norwegian, at any rate) now available in a searchable electronic form at the University of Oslo.
Medieval Nordic Text Archive - Another work in progress, that promises soon to make available a wide variety of scholarly electronic editions of Old Norse texts.
Netśtgįfan - Collection of Icelandic texts including much Old Norse, and several of the sagas in their entirety. N.B. Old Norse texts are in modern Icelandic orthography.
Northvegr - Texts and Translations - As well as providing the scanned version of Zoėga (see below), the Northern European heritage Northvegr Foundation has a range of public domain texts available for download. These are of varying quality and usefulness (and tend, being out of copyright, to be on the old side). Neo-paganism / 'Asatru' / reclaiming the heritage of one's Teutonic ancestry is not an interest of mine, but the people behind the Northvegr site have a serious scholarly outlook, and their site is worth investigating for those with a purely academic interest in medieval Scandinavia.
Ordbog over det norrųne prosasprog / A Dictionary of Old Norse Prose - Homepage for the extremely important (if rather slow-progressing) new Old Norse dictionary project, based in Copenhagen.
Ragnarsdrįpa - the poem by Bragi Boddason ('inn gamli'), edited by Margaret Clunies Ross.
SagaNet- A major project that aims to digitize all Icelandic manuscripts and printed books dating from before 1900.
Skaldic Poetry Editing Project
Teach Youself Old Norse (1) - Haukur Žorgeirsson and Óskar Gušlaugsson's introduction to Old Norse is incomplete (and I'm not sure if they update the pages any more), but it's got some useful and fun stuff on it, including Old Norse cartoons and sound files of readings.
Teach Yourself Old Norse (2) - Tarrin Wills's site (designed for the use of his University of Sydney students) has the best online grammar of Old Norse you're likely to find.
Zoėga: Concise Icelandic Dictionary online - Scanned text of Geir T. Zoėga's 1910 dictionary of Old Norse (now back in print from University of Toronto press: available from amazon) which isn't awfully good, but which is better than nothing.