ReFX Nexus 2 Expansion - SID
If anything deserves to be called "cult", it's the C64's SID-soundchip. 200 (!) presets give you access to the original sound, arps, and drums of that past era, partly created by using an original C64. All sequences of the mp3 demo are arpeggio-sequences played by NEXUS2.
This is a must-have not only for nostalgics - SID also creates perfectly massive sounds for weird electro-styles!