Monitor plugin for free (newsletter subscription) from Press Play.
You can get a Moog emulation for free from IK Multimedia if you subscribe to their newsletter until Dec 30th.
You can choose your own price (also free is possible) for 2 interesting FX plugins from Freakshow Industries. You decide.
DFR-76 is a FREE plug-in that contains 27 HQ playable instruments ranging from bass, keys, plucks and more. Here are some audio demos:
You can download 180 high-quality samples with sounds recorded from historic computing devices for free, following the link at the blog of Motion Soundscapes.