Malpertuis (1971),
Brussels by Night (1983) and
Crazy Love (1987) are musts - surely they have been extensively covered on these forums (or at least, they should be). But that's hardly cult, they're in a league of their own. Fantastic films and Cinematek's dvd's come with English subs and packed with extras.
Crazy Love was also released by Mondo Macabro, an off-beat dreamlike, visually dazzling Bukowski-adaptation (strongly influenced by The Outsiders and One from the Heart). Honestly, they're all favs, can't think of anything but superlatives for these three films.
They're part of "The Flemish Film Chronicle". More details and specs:
MalpertuisBrussels By NightCrazy Love