as the mega has all female headers onboard, does anyone know if there exists a sort of pin header that would enable me to connect an existing ribbon cable end to the board itself? standard straight pin headers seem like they'd be too short on the one side to do so and i've searched but not really found anything. if i can do this without resoldering a 26 pin ribbon... yeah.
The sort or ribbon connectors you have seen is called an IDC (insulation displacement connector), and is very convenient.
Unfortunately this will not work well with the arduino because the pin spacing is a single row of 0.1" pitch pins. IDC uses (mainly) 0.5" to connect to a double row of pins on a 1" pitch.
Solder normal headers back-to-back.
If necessary split the ribbon cable and use seperate IDC sockets to handle the odd header spacing.
There are single-row IDC connectors on .1" centers. I have a small collection of premade cables I found at a surplus store that I've used for things like connecting to LCDs.
You can do direct soldering to headers to make cables, but I avoid that whenever I can, because it's hard to make them sturdy. If there's room for it, what I prefer is to use a small piece of stripboard, and solder both right-angle headers and wires to it, to make a sort of custom connector. It's a stronger connection, and you can add some strain relief to it.