The final build of Ubuntu 9.10 (dubbed Karmic Koala) has been spotted on Ubuntu's servers for distribution. However, you may find due to the sudden slamming your download might be painfully slow, so if you can hit it up via BitTorrent you may have it much sooner.
From our own experiences, and those of commenters, the final release of Karmic Koala will generate enough traffic to seriously slow, if not entirely 404, Ubuntu.com's web servers. If you're good with BitTorrent downloading, it's likely your best bet for today. Grab the copy you need-for most users, that's the ubuntu-9.10-desktop-i386 image or torrent-and leave your torrent client running for a bit to help spread the open-source vibes.
Already running the beta or release candidate? Assuming you've been keeping up with your updates, you're already running the final version by now. If updates happen at a molasses pace today and tomorrow, try switching to a mirror server to move things along.
If interested, LifeHacker also recently took a look at 9.10 in beta form, posted an "emergency key" restoration tip and also directed non-Ubuntu 9.10 users where to go for the new icons and wallpapers.