Another one in the old but gold category. Mammut is a cool sound manipulator tool.
For some oldskool vibe: Combo Model F is a freeware virtual combo organ, modelled after a well-known combo organ from the 1960s.
Using the power of bouncing and resampling, you can consolidate your non-playable layers and stacks into one epic, playable sound. Soundbrige explains.
Very nice Reaktor FX ensemble to 80s-fy your songs. Free from the NI Reaktor User Library.