Dell Latitude E6400
The Dell Latitude E6400 is an alternative to the X200/T400 laptop, because it is is possible to install libreboot on it. Unlike X200/T400 etc, the Dell Latitude E6400 can be flashed from software, from vendor BIOS to coreboot/libreboot. Of course it is possible to install Trisquel GNU/Linux on it, too.
Hardware
The Dell Latitude E6400 has the same hardware gen as X200/T400 (GM45), so it's reasonably fast for many types of users. The Latitude E6400 has a similar screen/keyboard quality like the X200/T400 and also comes with a track point. It is more popular than ThinkPads, so the chances are good to get one.
There are variants with nvidia or intel graphics.
Read the hardware info page from the libreboot project here: https://libreboot.org/docs/hardware/e6400.html
Flashing the BIOS for the E6400
The board can boot entirely free software in the flash. The hardware is similar to that of ThinkPad X200, T400 etc where no-ME setup is possible.
Read the installation page about flashing here: https://libreboot.org/docs/install/e6400.html
Note: Software flashing is possible! (no disassembly needed)