Ok, here's the final deal, a friend also helped me out with the math.
I will drive 2 x 74HC595 in series, so I can get 16 outputs.
Them I will drive those 16 outputs directly to 2 x ULN2803A
On each output of the ULN2803A, I will put a 100 ohm resistor + UB LED. (2.3Vf 20ma)
In my tests it works perfectly. And if I want a second LED to make it more bright, I just put another 100 ohm resistor and add in parallel.
Now I need to get some White-Frost Plexy to test how this will look like.
Here's something some guys did that are similar to my idea. But I plan on using RED-Only LEDs (Ultra Bright) and a 4 x 4 pattern instead.http://e2e.ti.com/group/microcontrollerprojects/m/msp430microcontrollerprojects/447779.aspx
The difference is that in my project, each square will be touch-sensitive. ;-)