I've been playing with the Lomo filter for the Gimp from Goose24 after reading a tutorial on faking a lomo look (via The Tao of Mac). Take any boring looking picture with flat contrast, put it through the filter, and out pops a much nicer looking snap.
It seems it works best on pictures that haven't necessarily been through an 'auto-levels' process, and flat areas of colour obviously help, where you can see the effects of the slight vignette. Throw-away, but nice.
Update: It looks like I've lost those pics after a spot of unexpected data loss. Easy come, easy go!