Is there anything simular to Eyefinity for Ubuntu? More the idea of turning 3 smaller monitors into one big monitor
The newly released (proprietary) 10.7 Catalyst drivers from ATI specifically support Eyefinity under Ubuntu 10.04 (Lucid).
The proprietary NVidia drivers also support multiple monitors rather well, allowing you position them in relation to one another.
In theory the Monitor Preferences also supports configuring multiple monitors in this way, but reports on the Ubuntu forums are mixed and I have no way to test this personally.