Coupon UUWZ002 seems to be dead, even though Budget's website still takes it. I used it twice on two recent one-way rentals for an intermediate car and I did not get an upgrade.

However, I have just found a BCD and coupon code for a free upgrade on Office Depot's Worklife Rewards partner offers page. Worklife rewards is like a grocery store loyalty card that anyone can sign up for free.

Save up to 25%, plus a one car class upgrade

Save up to 25% on your next rental. Plus, get a one car class upgrade.
To save up to 25% on your next rental mention BCD: S164586. To receive a one car class upgrade mention Coupon: UUCZ024

Offer available in the U.S., Puerto Rico, and Canada.

Up to 25% Off next car rental: S164586 Terms and Conditions The savings of up to 25% applies to a Budget leisure daily, weekly, weekend or monthly rate and is applicable only to the time and mileage charges of the rental. Taxes, concession recovery fees, vehicle license recovery fee, customer facility charges ($10/contract in CA) and fuel charges are extra. Optional items such as LDW ($22.99/day or less) fees and other surcharges may apply and are extra. Offer is available for U.S. and Canadian residents only for rentals at participating locations in the contiguous U.S. excluding the New York Metro area. Offer may not be used in conjunction with any other coupon, promotion or offer. An advance reservation may be required. Car rental return restrictions may apply. Offer subject to change without notice. Holiday and other blackout periods may apply. Renter must meet Avis age, driver and credit requirements. Minimum age may vary by location. An additional daily surcharge may apply for renters under 25 years old. Discount valid on rentals checked out no later than 12/31/11.

Single Upgrade: UUCZ024 Terms and Conditions Coupon valid for a one time, one car group upgrade on an intermediate (group C) through a full-size four-door (group E) car. Maximum upgrade to premium (group G). Offer valid on daily, weekend, weekly and monthly rates only. The upgraded car is subject to vehicle availability at the time of rental and may not be available on some rates at some times. Coupon valid at participating Budget locations in the contiguous U.S. Coupon must be surrendered at time of rental; one coupon per rental. A 24-hour advance reservation is required. May not be used in conjunction with any other coupon, promotion or offer. For reservations made on budget.com, upgrade will be applied at time of rental. Renter must meet Budget age, driver and credit requirements. Minimum age may vary by location. An additional daily surcharge may apply for renters under 25 years old. Fuel charges are extra. Rental must begin by 12/31/2011.