This module from Frozen Wasteland is my favorite for this purpose. It wraps up what I think are the essential features for a fully flexible Karplus Strong synth:
- V/Oct tracking (standard delays don’t)
- Processes external input (many KS modules don’t), but will make its own impulses using the trigger input (many KS delays don’t, although you can just roll your own so no big deal)
- Includes send/return jacks so you can get inside the feedback path
I’m not aware of another module that does all three. If you really want to get into waveguide synthesis, getting inside the FB loop is where the power is IMHO - e.g. you can put another delay line inside the FB loop. String Theory also includes a filter in the FB path (not uncommon), a ring mod in the FB path (unique but not always useful), and a “grains” control, which is also unique but, unlikely ring mod, it’s more subtle, allowing for organic-sounding variation between plucks.