If speed is not so important (or when memory usage is) the following should work as well:

unsigned char FlipBits(unsigned char InVal)
{
unsigned char BitMask1=0x01;
unsigned char BitMask2=0x80;
unsigned char Result=0;

while(BitMask2>=1)
{
Result+=(((InVal&BitMask1)>0)*BitMask2);
BitMask1<<=1;
BitMask2>>=1;
}
return(Result);
}