Here we go, you can now download the update directly if you don't want to wait for the OTA.
The links are the official ones from the Google-Servers. There is absolutely no difference if you wait for the OTA and you will receive new updates as usual.
Nexus One: http://android.clients.google.com...GRI40-from-FRG83G.81304b2d.zip
Nexus S: http://android.clients.google.com...GRI40-from-GRH78.e0b546c4.zip
If you wonder on how you can update the Nexus One manually, Androidcentral has a nice video. You can watch it after the jump.