Throughout 2010, my favorite car rental bonus was 3000 US Airways miles on a 3-day (or longer) Avis car rental. And even when American had a similar offer, I stuck with the US Airways bonus because it overlapped with their ‘Grand Slam’ promotion, so each Avis rental also counted towards their 100,000-mile offer.

The offer was originally scheduled to run through March 31, 2011 but it was extended through March 31, 2012. The offer says it’s intended for US Airways Dividend Miles elite members, but I’m not one and can confirm that it works for anyone. You just have to use coupon code MUAA044 and provide your Dividend Miles number with the reservation.

The promo also promotes the US Airways ‘discount code’ (AWD) but you do not need to use this in order to get the bonus miles. And I generally don’t. My own corporate discount code gets a reasonable price much of the time, and it also gets me credits in the Avis Corporate Awards program where every 15 rental days earns a free rental day. So I get to double dip that way.

I get excited, then, when I have a 3-day car rental. I usually have one- and two-day rentals. So I tend to credit those to Virgin Atlantic, which offers a flat 1000 miles on a 1-day rental.

Sure, Avis doesn’t always have the very best rates or the best mileage deals. But I’m an Avis junkie because they treat me well (elite status) and so they get my business, the rest is just bonus as it were.

Still, for a more comprehensive look at currently-available offers, it’s worth booking the FrequentFlyerBonuses page which catalogs a pretty good up-to-date list of mileage offers for car rentals, sorted by rental agency.

And of course for the best rates, try AutoSlash. It’ll apply publicly available coupons to find you the best price. Most of the time it’s not all that different than what you’ll find elsewhere, but the real trick is that they’ll keep checking rental rates daily and if the price drops they’ll adjust your booking automatically — and they’ll keep checking other agencies as well, and invite you to switch if they find a better deal elsewhere.

Avis doesn’t participate with AutoSlash, so you won’t see their rates when you search. But AutoSlash has a pretty neat feature where you can provide them a car rental booking you made elsewhere and they’ll still track it for you (this feature does include Avis). So even if you don’t originally book through AutoSlash, they may still be able to save you money on your rental.

Not as much money, perhaps, as just booking through Hotwire or Priceline — which sometimes offer really good deals if you’re willing to prepay, and I tend to prefer Hotwire which tells you the price and vehicle type but not rental agency though Priceline sometimes will beat Hotwire by about 10% — but of course Autoslash bookings aren’t prepaid, there’s no credit card required, you can totally walk away…

Even rental cars can help rack up the points towards your next trip!