IP Spoofing with TCP over the open internet is impossible because of the three-way-handshake. So you are limited to ICMP/UDP services or attacks on services available over the local LAN. The local lan is an issue if you are able to sniff the network. So this is a problem if you are on a broadcast network or using ARP poisoning on a switched network. ARP poising is also a spoofed attack.
A good example of a spoofed icmp attack is the Smurf DoS Attack. The UDP variant of this DoS attack is called the Fraggle attack. (Who names these!?!??) Also it should be noted that these attacks are old its unlikely that you'll find a vulnerable network.
So in conclusion IP spoofing has a very limited scope. Because Its an attack that has been taken into consideration and its easy to prevent.