In terms of 3.2 boards, there is this board, which breaks out the 3.3v and ground for each of the digital pins, and 3.3v, digital ground, and analog group for the analog pins:
But from a functional point of view, in theory I like the KurtE board (first link in Paul's posting). While I have it, I haven't yet soldered a Teensy to it. But the way I tend to use Teensys, it would be nice to have breakouts for:
Parallel 24 pin rows on each side of the board, to allow for jumper wires to do random connections.
4 or 5 pin breakouts for each of the serial devices (3.3v, digital ground, RX/TX, and possibly VIN).
4 or 5 pin breakouts for each of the i2c ports, along with a place to add the pull-up resistors for each bus (3.3v, digital ground, SCL/SDA, and possibly VIN).
SPI breakouts for SPI0 (3.3v, digital group, SCLK, MISO, MOSI, plus at least pins 9, 10, 15, 22, 23 (these are the accelerated pins, and of course possibly VIN)
SPI breakouts for the other SPI busses, with a few pins.
Breakout to allow for an amp to be connected to the DAT0/DAT1, and output to speakers/headphone jack.
Access to the bottom and inner pins.
Others probably want breakouts for CAN and I2S connections.
However, if you fully populate a board like that, it likely will be too big and expensive for general use.