Xsane. Xsane has many options, has a style that does not integrate into the current Ubuntu desktop and does not allow scanning from within applications. In Karmic it was proposed to peplaced Xsane with the application Gnome-Scan, but Gnome-Scan was not found to be stable enough.
Robert Ancell's application titled Simple Scan is basically a frontend for SANE - which is the same backend as XSANE uses. This means that all existing scanners will work and the interface is well tested. However, this does not rule out changing the backend in the future. Besides a much cleaner interface, Simple Scan will also have a GTK+ interface that integrates nicely with the Ubuntu desktop.
Simple Scan is under heavy development, but hopefully Robert will have something solid, slick and intuitive to ship in Ubuntu 10.04.