If you look in the log file in /var (for xorg-x11 it is Xorg.0.log, for XFree86 I believe it is xfree.0.log or something similar) and read through the output you can see what modules were loaded. To go one further, if you do a "grep LoadModule Xorg.0.log" it'll output just the modules loaded.
For example, from my laptop:
Code:
j_shaw@jshaw /var/log $ grep LoadModule Xorg.0.log
(II) LoadModule: "bitmap"
(II) LoadModule: "pcidata"
(II) LoadModule: "record"
(II) LoadModule: "extmod"
(II) LoadModule: "dbe"
(II) LoadModule: "dri"
(II) LoadModule: "glx"
(II) LoadModule: "GLcore"
(II) LoadModule: "xtrap"
(II) LoadModule: "freetype"
(II) LoadModule: "type1"
(II) LoadModule: "radeon"
(II) LoadModule: "ati"
(II) LoadModule: "mouse"
(II) LoadModule: "kbd"
(II) LoadModule: "radeon"
(II) LoadModule: "vgahw"
(II) LoadModule: "int10"
(II) LoadModule: "ddc"
(II) LoadModule: "i2c"
(II) LoadModule: "fb"
(II) LoadModule: "ramdac"
(II) LoadModule: "xaa"
(II) LoadModule: "theatre_detect"