I just use "Gunk Bug Remover w/ Wax". Works like a charm. All you have to do is spray it on your bumper, let it sit for about 5 minutes, and with a sponge wash with warm water. Removes all the dead bugs and their guts effortlessly without the risk of scratching your clearcoat.
Amazon.com: Gunk BUG33 Bug Remover with Wax - 33 fl. oz.: Automotive