If I recall correctly there was a smaller version of GT5 / Prologue for the PSP, you could connect your PSP to your PS3 and download your garage or something along those lines. Because of the way the PSP version was made the cars were transferred as Standard cars, so there are some Premium cars that have Standard dopplegangers that are a throwback to the PSP version.
So far I've seen the TVR Tuscan and Tamora, Chevy Camaro Z28 and Mercedes 300 SL showing available as standard cars in the OCD (and have brought them with both my accounts). I think there are others but I don't know what they are (could probably search GTPlanet or google to find out), I do recall hearing rumours of a standard Ferrari Enzo at one point though.