I loved Frankenpod v1, but its main issue was build quality. The hot glue broke down after a while, requiring frequent repairs, and I also missed the ability to sync the player with iTunes (the player showed up as an external drive where you can drag and drop music onto it; some people prefer this system, I personally like to use iTunes). This reminded me about the solid state iPod Mini hack.
The original iPod Mini CF Hack
It turns out that the connector in the iPod Mini to its 4gb microdrive is the exact same connector used to interface with a compact flash card. This meant that you could easily replace the drive with a CF card, making the iPod solid state. Why do this? The reasons are twofold: more space (large flash memory cards are exceedingly cheap) and increased battery life (CF cards have no moving parts, so it takes less power to use them).
Since iPod Minis stopped being sold around 2006, you can pick them up for relatively little money. I went ahead and bought one, along with a 32gb CF card and a higher capacity after-market battery.
Our helpless victim
Unlike Frankenpod v1, this hack required little actual hacking. The only snag I encountered was when replacing the battery. The iPod I bought was refurbished, and the seller had soldered in the original battery to connector. Since I couldn't easily remove the original battery, I ended up snipping the cables and soldering the new battery in. I then pieced everything together and plugged it into my computer.
The original battery
iTunes may immediately recognize the device, but the first thing you should do is reformat the drive. I found this easiest to do in Windows without having iTunes installed. The drive should mount and you can reformat it to whatever the default format Windows suggests (FAT32?). Once reformated, plug the device into a computer with iTunes on it and iTunes should tell you that it needs to reflash the firmware onto the device. Once flashed, you're good to go!