Google's special site for the 10th birthday shows 17 of the most interesting homepage interfaces and Philipp Lenssen analyzes some of them. My favorite Google homepage is the one from April 1999 which only included a search box, two buttons and a link to "More Google!". If you like it, there's a slightly different version at google.com/ie_rsearch.html.
Google linked to many pages that no longer exist, but they're still available at Internet Archive:
* some credits from 1998
* press coverage from 1998-1999
* older versions of Google's logo
* Google's affiliate program
* an old Google tour
* the special Katrina page.