Recipes in online history
http://www.astro.cf.ac.uk/misc/recipe/introduction.html
The original Usenet Cookbook, compiled in 1994, from recipes posted to alt.gourmand.
http://www.recipesource.com
This is what used to be SOAR, the Searchable Online Archive of Recipes at U-C Berkeley, one of the oldest online collections, dating to 1995. They now have some 70,000 recipes.
Rec.food.cooking archives
The bulk of the archive of recipes from the Usenet group rec.food.recipes is, sadly, under the control of a onetime moderator who is now charging a fee to join her "Recipe Club" for access to most of them.
Various subsets:
http://www-2.cs.cmu.edu/~mjw/recipes
http://www.cdkitchen.com/rfr/index.php
http://www.netproxy.com/recipes/recipes.html