Some of last year's biggest winners aren't showing any signs of slowing down in 2010.

From resurgent automaker Ford (NYSE:F) to comeback kid Sirius XM Radio (NASDAQ:SIRI), many of the stocks that thrilled investors by doubling, tripling, or taking even bigger steps through 2009 are off to races again this year.

Take Dollar Thrifty Automotive Group (NYSE:DTG), for starters. Auto rental agencies were scorchers last year after being left for dead in 2008. Dollar Thrifty and Avis Budget (NYSE:CAR) appreciated several times over after bottoming out early last year. In Dollar Thrifty's case, the stock that began 2009 priced at a mere $1.09 closed out the year revving up to $25.61.

Dollar Thrifty now finds itself fetching $27.58. A nearly 8% gain may not seem all that scintillating, but keep in mind that we're just six trading days into the new year. Whole Foods Market (NASDAQ:WFMI), Ford, and Sirius are off to even better starts in 2010.

Company

2009

2010

Ford

337%

21%

Sirius XM Radio

400%

15%

Dollar Thrifty

2,250%

8%

Whole Foods

191%

8%

Source: Yahoo! Finance.

The momentum is impressive, since this could have been a logical time for many giddy investors to cash out. Instead of a hefty capital gains hit in 2009, many could have punched out at the start of 2010.

Why are they still hanging on? Well, the prospects are a whole lot brighter for these four companies now than they were a year ago.

Ford hit a new 52-week high yesterday. Technically speaking, it's closer to a 250-week high, since Ford hasn't traded this high since March of 2005. It's hard to bet against the automaker, especially after its head-turning 33% surge in December sales.

Sirius XM Radio had a prosperous 2009, particularly in the latter half of the year, when subscriber growth resumed and cash flow growth accelerated. Like many of last year's winners, Sirius XM had the luxury of an easy starting line -- its stock began the year at a just $0.12 a share -- but its surprising breakeven third-quarter results and renewed optimism for auto sales, where most of its new subscribers are coming from these days, find the satellite-radio monopoly sitting pretty.

Analysts see Dollar Thrifty earning $1.52 a share this year. Yes, it's expected to earn more than its entire market cap at the start of 2009. An economic recovery has lifted hopes for upticks in corporate and leisure travel, and Dollar Thirfty is a clear beneficiary.

Whole Foods is another company positioned for a big bounce if the economy continues to improve. Shoppers cut back on expensive organic groceries during the recession, but they should storm back soon.

So why are 2009's winners among the stocks with the healthiest starts in 2010? That's easy. They're earning it.

Whole Foods Market and Ford Motor are Motley Fool Stock Advisor picks. Try any of our Foolish newsletter services free for 30 days.

Longtime Fool contributor Rick Munarriz is a subscriber to both Sirius and XM. He owns no shares in any of the stocks in this article and is also a member of the Rule Breakers analytical team, seeking out the next great growth stock early in its defiance. The Fool has a disclosure policy.