Bands that broke up too soon:
Clockwork - one ABSOLUTELY AMAZING album then they broke up, and they all disappeared.
Dali's Dilemma - again, one and done, but at least they've stuck around in other bands.
Ice Age - Two solid albums before unsuccessfully selling out.
Power of Omens - Death of bassist
Bands that don't record often enough:
Arena - about 5 years between albums lately
Bruce Dickinson solo - Way to awesome to stop
Enchant - it's been almost 7 years
Shadow Gallery - yeah, they released an album last year, but the last three albums have been 4+ years apart
Symphony X - Two albums in last 8 years, although if they release another album as poor as Paradise Lost I won't care too much any more.
Peter Gabriel. Anywhere between six and ten years for a proper studio album.