I got one of my all time favorite synths, Eccentrix, from the Reaktor User Library. There's also some fantastic effects and drum machines (or "grooveboxes."
It's worth either reading the manual or watching Groove3's excellent course on Reaktor basics to understand how the snapshot system works. Snapshots are Reaktor's idea of presets and they have a tendency to confuse the heck out of new users, especially with regard to making and saving your own. It's not as intuitive as it should be tbh.