Cadillac (search) and Rolls-Royce (search) are in — but Lexus is out. Jacob the Jeweler (search) is hot — but Burberry and Timberland are not.

A new study of brand mentions in songs shows what's cool among the hip-hop crowd — and how fast tastes change.

So far this year, 59 different brands have been mentioned 645 times in Billboard Top 20 tunes (mainly hip-hop), according to a survey by San Francisco-based marketing firm Agenda, Inc.

Topping the talked-about list this year is Cadillac, followed by Hennessy, Gucci, Rolls-Royce, Nike, Mercedes (last year's top car), Jaguar and MTV.

"This is a window into pop culture," says Lucian James, president of Agenda Inc. "It's fascinating to see the brands rise and fall over time."

The big loser of 2004 is Burberry, which came on strong last year, scoring 42 mentions from rappers such as Ludacris, who rapped about a high-flying player who was "smelling like Burberry cologne" on Missy Elliott's "Gossip Folks."

Last October, a newspaper reported that Burberry didn't want to be associated with rappers, and apparently they listened.

So far in 2004, the label has only been mentioned four times.

On the other hand, Porsche (search), which lost its streed cred for a while, is back in 2004, including in Jay-Z's hit "Dirt Off Your Shoulder."

Brands that get mentioned in insulting lyrics include Kmart, Holiday Inn, Cool Whip and Payless.

One of the biggest surprises of the year is Rolls-Royce, which has 26 mentions so far.

"The Rolls used to feel dated, but they've updated their models and given the brand a new life," James says.

"It seems to have a direct appeal to the P. Diddy crowd."

You can hear all about it in this week's number-one song "Lean Back" by the Terror Squad, which gives props to the Rolls Phantom, as well as the BMW 740, Gucci sweaters and Gulfstream jets.

Hip-hop songs mention far more labels than rock or pop ones, which doesn't surprise hot rapper Kanye West, who touts 19 different brand names in the four hits he's had this year.

"Black people have always liked to associate themselves with hot brands," West tells the Post.

Name-dropping is also "a good way to make a point," he says. An example is West's "All Falls Down," a satire of materialism in which he raps about people who "can't even pronounce nothing, [so] pass the Versace."

Sometimes it also just sounds cool.

"Like when P.Diddy was talking about 'Pass the Courvoisier,'" West says.

"That was just something hot to say — better than 'pass the beer.'"

When a rapper mentions a brand name in a song, it has an effect on the marketplace.

"Cadillac wasn't cool for so long," says Amanda Freeman, vice president of the New York trendspotting firm Youth Intelligence.

"But then some artists started picking up on it and rapping about it, and now the Escalade is a hot car."

With that kind of influence, it's no surprise that rappers get offers from companies to exchange product placement for money.

"I've had lots of companies come up to me, saying, I'll give you a thousand to mention this, five thousand to mention that," Kanye West says.

"I didn't take it, but a lot of rappers do.

"I can always tell when I hear it in the song, because I'm like, 'Why are you mentioning that product here?' Sometimes it's just obvious."

Petey Pablo even bragged about getting cash for props in his hit, "Freek-a-Leek:

"Now I got to give a shout out to Seagram's gin," he rapped.

"Because I'm drinking it, and they're paying me for it."