Actel devices are often used because they use flash memory for the configuration, which makes them usable in situations where RAM may be untrustworthy for something so important (e.g. where you can get bit-flipping due to ionising radiation).

They also make properly rad-hard FPGAs, although these are ridiculously expensive (I've heard that if you are looking at building more than ~10-15 units, an ASIC may actually be cheaper).

Edit: I should add that you could still use Xilinx and Altera devices in these situations, but you really need some way of mitigating the problem -- such as TMR memory.