Yes, I also believe every animal on the face of the earth perished in the Flood.
That said, theologians have many theories on why there were giants after the flood, but Scripture doesn't explain it clearly. As was suggested by another Freeper on this thread, the DNA of the sons' wives might have been tainted.
But, however it happened, there were giants (descendants of the Nephilim and the Fallen Angels) after the Flood.