I'm a bit surprised this thread hasn't generated more interest. Heck, I keep consulting it myself when I need to make one-way car rentals reservations for myself and friends/family.
I've got another Hertz number to add: 1813168. Reportedly Car & Truck magazine (never heard of it). It can get you a lower base rate than the Car & Driver number above, but watch for potential per mile charges.
And I'd love to see folks add their own discounts. Having all the one-way codes in one place certainly makes it easier for me. Thanks.