Using a 800x480 LCD with Raspberry Pi

Is simple. Into /boot/config.txt, put:

#increase HDMI signal strength (just a black screen if not set!)

config_hdmi_boost=4

#remove black borders

disable_overscan=1

#set specific CVT mode

hdmi_cvt 800 480 60 6 0 0 0

#set CVT as default

hdmi_group=2

hdmi_mode=87

My LCD is the Lilliput 669GL -- works like a charm.