The default Ubuntu Flash Player was really unstable on my machine. That’s why I went searching for a more stable 64bit version. On Ubuntu 10.04 I used the file libflashplayer-10.0.45.2.linux-x86_64.so.tar.gz that circulated on the web. On 11.04 I found out there’s a nice repository with the latest x86_64 version. Thanks to SevenMachines it is really easy to install.
add-apt-repository ppa:sevenmachines/flash apt-get update apt-get install flashplugin64-installer