May want to look into General Jimmy Doolittle.

After his famous raid on Japan he was promoted to Brigadier General (skipping full Colonel) and sent to command the 15th Air Force in North Africa in Sept 1942. Then after a promotion to Major General to Italy to command 15th Air Force in Italy with command over the entire Med.

Finally to LTG and to England to command 8th Air Force in March 1944. During this time he also continued to fly bombing missions as well!

I imagine you can find quite a few examples in the navy. The USS "Laffey," for example, was decorated for combat at D-Day (where she was hit by a German shell) and multiple times in the Pacific, where she survived the most ferocious kamikaze attack in history. Her captain, Julian Becton, served in the Pacific, Europe, and then back in the Pacific. He wrote an excellent book about his experiences with the "Laffey"--"The Ship That Would Not Die." The ship recently underwent a massive restoration and is docked in Charleston, South Carolina.

While no US divisions served in both ETO and the Pacific, as previously mentioned it wasn't unheard of for ships and pilots to do so.

One particularly interesting case is that of Sgt Ben Kuroki of the US Army Air Corps/Forces. He was born to Japanese immigrants in Nebraska, and became one of the first nisei to enlist after Pearl Harbor. He ended up as a turret gunner on a B-24 Liberator, flying 30 missions before being lightly injured by flak.

After healing from his wounds, he specifically requested to be assigned to the Pacific Theatre, but it took the intervention of higher-ups to get that approved. He then flew 28 missions over Japan as a member of a B-29 crew, becoming the only American of Japanese descent to do so in WWII.

Source: a documentary about him entitled Most Honorable Son that airs on PBS every now and again, and this article here.

Another general is Stanley E. Reinhart who commanded the 25th div. artillery defending Oahu and served at Guadalcanal in 1942. After returning to the US, he organized 65th Infantry Division, which shipped to Le Havre and fought in Patton's 3rd Army. Reinhart then served as military commander of US-controlled zones in post-war Austria.

Semi-related question: is there a way to find WWII service records online? I seem to remember my grandfather talking about serving in both a tank in North Africa and on a B-25. Wikipedia says the B-25s where mostly deployed to Pacific.