

According to Google engineer, Dan Morrill, the AOSP Source Code for Android 4.0/Ice Cream Sandwich will be released shortly after the Samsung Galaxy Nexus goes on sale. Here's his quote,
This is in-line with past behavior from Google for new Android releases, so it shouldn't come as a surprise. Several sources practically confirm that we can expect the Galaxy Nexus to hit the streets in mid-to late November, which would mean we could probably see ICS before Christmas. It sounds like developers are going to have a busy holiday season.To reiterate, these servers contain only the ‘gingerbread’ and ‘master’ branches from the old AOSP servers. We plan to release the source for the recently-announced Ice Cream Sandwich soon, once it’s available on devices.
Source: AndroidPolice