"Ford Ka Helps Billie's Driving Ambition!" "All Saints Choose Chart-Topping Jeep Grand Cherokee!" "Slade to Tour With Ford Minibus!" Manufacturers are always eager to tell us about their latest sponsorship hook up with the pop star of the moment (and Slade). But standing amid the throng watching All Saints collect the keys to their new wheels at last year's Motor Show, I couldn't help but wonder whether a glorified mini-van was appropriate transport for a group of supposedly cool and foxy international pop stars. And All Saints aren't the only sell-outs.

Take a look at the cars most pop stars drive, or are driven in, these days and, with the exception of Ferrari fan Chris Rea (who I'm not sure counts anyway) and Prodigy's Keith Flint, who drives a monster of a TVR, mundanity rules. Hang around outside the Brits and you'll see that the Mercedes S-Class, or worse the Toyota Previa (for second-string boy bands), are the standard pop star transport.

Maybe today's artists can ill-afford to be seen endorsing fossil fuel-burning extravagance, as Jay Kay has found to his cost when pilloried for his conflicting environmentalism and a penchant for 12mpg Lamborghinis. Whatever, things were certainly different in the 50s and 60s, when no artist would venture out in anything less than a fur-trimmed Roller with gold-plated hub caps. The best of these fabulous vehicles can still be seen in two extraordinary car museums, one at the Liberace Foundation in Las Vegas, the other at Elvis's home, Graceland, in Memphis.

Automobiles may have been at least partly to blame for Elvis's slothful ballooning, but he still loved them. "The first car I ever bought was the most beautiful I've ever seen," Elvis once said. "It was secondhand, but I parked it outside my hotel the day I got it and stayed up all night just looking at it. The next day it caught fire and blew up on the road."

I suspect it may have been suicide. The car knew what he would have done to it had it lived. The first new car he bought, soon after his first string of hits on the Sun record label, was a 1956 Cadillac. According to legend, Elvis went into the showroom clutching a pound of grapes and squeezed the fruit on to the bonnet of the demonstrator. "That's the colour I want my Cadillac, thangyouverrymuch," he said. It was the only known instance of Elvis wasting food.

That Cadillac is the first car you see as your eyes adjust to the reverently dimmed light inside the museum. The rest of the collection is arranged in a horseshoe around a re-creation of a drive-in movie theatre. Filmgoers watch selected car moments from Elvis's movies on a continuous loop, while parked in authentic 1957 Chevrolet seats.

The collection is by no means complete - Elvis's legendary gold Caddy is on display at the Country Music Hall of Fame in Nashville and other Elvis-mobiles are often advertised on the internet. As his wealth snowballed he began buying new cars, each of which he would personalise with the same good taste that judged the living room ceiling to be an appropriate place to lay shag pile. Cadillacs, Jeeps and Harley Davidson motorbikes abound throughout the rest of the museum, each with either a spangly silver or a bilious pink paint job to mark them as the property of the King. Occasionally Elvis inadvertently allowed good taste to obscure his better judgment and bought a European machine. But even then he either chose a dud (his black Ferrari 308 GT4 is about as desirable in Ferrari circles as rust), or irretrievably disfigured his purchase with an ill-advised piece of customising (as with the vile blue leather in his Rolls-Royce Silver Cloud).

Elvis didn't reach his zenith until the 70s, and neither did his cars. I didn't know whether to laugh or cry when I reached the half way stage of the tour and the centre piece of the exhibition: a brace of Stutz Blackhawks.

Even in standard trim Stutz Blackhawks are ostentatious. The first one ever made was originally ordered for Frank Sinatra in 1971; Elvis charmed it from the dealer for $26,500 (Sinatra's response is not recorded). Frustratingly, an assistant wrecked that car while on his way to wash it shortly after Elvis took delivery (it was later repaired). Undeterred, the King bought another of the Pontiac-engined monsters and had its interior plated with 18-carat gold. Both are on display at Graceland.

As if Elvis's cars hadn't suffered enough, he even tried to murder one of them. As is the custom with highly strung, mid-engined Italian supercars, Elvis's rare and beautiful De Tomaso Pantera refused to start one morning. Instead of calling a breakdown service, as you or I might, he simply pulled out his gun and shot it.

By the standards of what Wladziu Valentino Liberace did to his cars, Elvis's Pantera got off lightly. Las Vegas's Liberace Car Gallery is possibly the only car museum that could rival Elvis's for chintz and chutzpah. I took a cab there from the Strip and found, alongside the world's biggest rhinestone and more dodgy candelabra than Bermondsey market, numerous customised classics.

Take the priceless Rolls-Royce Phantom V Landau, smothered in tiny mirror tiles etched with a design of galloping horses. Beside it in the low-rise museum compound, ranged appropriately around a parking lot, sits a matching Baldwin grand piano. Or Liberace's Excalibur, a British confection based loosely (and I mean loosely) on the legendary Mercedes SSK. This one is covered from head to fender in Australian rhinestones (his favourite semi-precious rock).

Liberace, at one time the highest-paid musician in the world, didn't own a car until he was 30, when he bought an Oldsmobile 88 convertible - chosen because a piano has 88 keys. But once he bought that he was hooked, and embarked on an automotive spending spree untrammelled by notions of taste or restraint. As with Elvis, but sadly not today's off-the-peg stars, Liberace didn't stop once he'd bought a car. Even his more mundane machinery would be decorated with a piano key motif, or bedecked with his trademark candelabra. But Liberace's greatest automotive crime was that the only mileage his grand and costly cars accrued was in carrying their owner on and off stage to the applause of a sea of blue rinses.

As you wander around the rest of the collection, you cast incredulous eyes over a Rolls-Royce Silver Cloud with a striking red, white and blue colour scheme, in honour of America's bicentennial; a bastardised Beetle - "Volks-Royce" - part Roller, part VW; a customised London cab (Liberace was a committed Anglophile - or "insufferable snob" as they are known in the US); a 1964 Cadillac with diamond-studded candelabra, a bar with sterling silver cups depicting winners of the Kentucky Derby, and a TV and stereo; as well as dozens more motoring atrocities. As far as I'm concerned, it more than warrants its title of "Nevada's third most popular tourist attraction".

One man whose name crops up in both museums is George Barris, fabled customiser and creator of the original Batmobile. Barris painted Elvis's gold Cadillac, and also plastered Liberace's 1954 Eldorado with a chrome piano key design and used candelabra as (hardly pedestrian-friendly) bonnet ornaments.

It could be that today's pop stars need a man like Barris to pep up their garages. He could decorate Morrissey's Porsche with a fibreglass quiff; the Sterophonics' car could be swathed in sheepskin; or maybe Liam Gallagher would like a large pair of bushy eyebrows atop the windscreen of his Bristol.

I suspect my fantasies may all be in vain. Elvis and Liberace existed in an era more tolerant of such gaudy glamour. Perhaps, on reflection, it's best that way.

Graceland, Elvis Presley Boulevard, Memphis (001 901 332 3322); The Liberace Car Gallery, 1775, East Tropicana, Las Vegas, Nevada 89119 (001 702 798 5595)