If you want some really easy projects, just passive RC circuits for blur and sharpen inline with your patch cables would be fun, too! LZX IOs are buffered right ta the input and the output, so you'd be putting the RC directly between 2 buffers, so you shouldn't experience much in terms of gain loss. Just account for having 499R output resistors in series with the circuit when doing your calculations. http://www.2pif.com/high-low-pass-filter.php

The TVMF was based on the multimode circuit in the LT1228 datasheet, which uses 2x LT1228s. You get bandpass output from that, which can be nice. There's a 3.58MHz phase shifter circuit in the LT1256 datasheet I've always wanted to try out. It uses 3x LT1256 so pretty expensive to build, but could make a very nice composite video colorizer.

There's the Sandin IP differentiator. LT1256 and LT1228 datasheets both have good VCF circuits. Curtain uses an LT1228 for VC highpass and an LT1256 as voltage-controlled attenuverter (4 quadrant mult -- you can steal that from the C10 schematic) to process the filter output before blending it back in with the input. There's a full wave rectifier in there too, to get all the different edge modes. Highpass + original input signal = edge enhancement. Original input signal - highpass = blur.

 I just built a little passive inline filter per Lars' suggestion, but I needed to use 1nF instead of 1uF to get in the 100KHz range. I used a 10k pot as well, which makes the range about 15KHz to 300KHz. Works great!