Here is a small utility board - a simple buffer followed by a phase inverter. You can take the output from either stage. It can be very useful if you are adding a clean blend to a circuit that is inverting the phase.

I recommend putting this in front of your main effect, but keep in mind that not all effects will respond the same with a buffer in front. I didn't include polarity protection, DC filtering and an output capacitor since this is meant to be used together with another effect (not stand alone).

Here's something fun that I found at diystompboxes.com (original thread here).

It's a little circuit that converts your guitarsignal into MIDI language, so you can use your guitar with your favourite synths. :) It's monophonic, so it's not good for chords but works ok for single notes, leads, basses ect.

It requires a specific PIC chip and PIC programmer hardware (such as pickit2), software, and code (downloads at the bottom of the post) to be written onto the chip, so it's a bit harder to do then your regular stompbox. More info below.

This is what you will need:

• The PIC16F88 chip. It's an older 8-bit chip, but still easy to find (try ebay). The code is written for the chip so other PICs with not work.
  
• The hardware required is either pickit2 or pickit3. I borrowed a pickit2 from a friend, but you can buy them here. Pickit is basically a interface that connects to your computer with USB and lets you read/write/erase programs to the PIC chip. Keep in mind though that the chip-socket may not have the same pinout as the chip. I used a breadboard to jumper the connections, as shown here.
• There are alot of choices for the software (all free). I used PICkit 2 v2.60, but MPlab and PICgm Programmer are also good,
  
• Code! Download the required code below. Only one of them is needed. Try the second one if you are having trouble writing the code to the chip with pickit2.
  

Here's a good circuit if you want to avoid those clunky and expensive 3PDT switches and use a soft-touch momentary SPDT footswitch insted, or something else, like a push button switch.

One could argue that this one isn't really suitable for vero (tons of links...) or worth the effort, but I think it's nice for those extra special builds and it's also much cheaper than using relays. It does take a bit of space, but it can fit in a 1590B (depending on the size of the effect circuit).

Here's a small little circuit that I have had lots of uses from.