Took the binary solution already mentioned and removed the branching. Did some testing and it turned out to be 1.3 times faster than DeBruijn.
public static int Log2(int v)
{
int r = 0xFFFF - v >> 31 & 0x10;
v >>= r;
int shift = 0xFF - v >> 31 & 0x8;
v >>= shift;
r |= shift;
shift = 0xF - v >> 31 & 0x4;
v >>= shift;
r |= shift;
shift = 0x3 - v >> 31 & 0x2;
v >>= shift;
r |= shift;
r |= (v >> 1);
return r;
}