An amusing corollary of FLT is that the n-th root of 2 is irrational for n > 2.
For if (a/b)^n = 2 for some integers a,b, then a^n = b^n + b^n provides a solution to the Fermat equation ;).
Sadly, Fermat's last theorem is not strong enough to prove that the SQUARE root of 2 is irrational.