Compiled by Lex Vehicle Leasing, the survey of the predicted residual values of thousands of cars on its fleet covering a typical annual mileage of 60,000 miles found the Boxster will be worth £18,000, or 57% of its original cost new. In this year's Lex top 10, coupes and 4x4s led the way, with seven making an appearance, while the Audi TT, Jaguar X-type and BMW 3-series were among those that dropped off the list.
The new chart sees the Mercedes-Benz CLK and SLK in second and third places respectively and reinforces the manufacturer's reputation for stylish sports cars and superb build quality.
The highest entry this year is the Volvo XC90 while the Land Rover Defender has moved up two places to fifth position.
Steve Jones, pricing manager at Lex Vehicle Leasing, said: 'The Porsche maintains its desirability in the second-hand market, despite the earliest examples dating back to 1996. Nothing else can offer that combination of stunning good looks, supercar badge and Teutonic reliability.
'The introduction of the latest Mercedes-Benz CLK gives a strong residual premium over the outgoing model, as used buyers will be keen to snap up the first second-hand examples.'
Two Volkswagens, the Beetle Cabriolet and the new Polo, appear for the first time in the chart at number six and seven respectively, while the Mercedes-Benz E-class debuts on the list at number eight.
Jones added: 'Our 2003 list reinforces the link between new models and a high second-hand value. Everyone likes to have the latest model and as a result when a new car is introduced we forecast high residuals, which then fall away as the car gets older, except in the case of cars such as the Boxster.
'The Volvo XC90 and BMW X5 go one step further, having long waiting lists and in some cases making as much money at six months of age as their original cost new.'
He added: 'The Land Rover Defender still holds on to its top 10 status, despite its age and a whole host of new rivals.'
Lex residual value top 10
1 Porsche Boxster (1)
2 Mercedes-Benz CLK (4)
3 Mercedes-Benz SLK (3)
4 Volvo XC90 (new entry)
5 Land Rover Defender (7)
6 VW Beetle Cab (new entry)
7 VW Polo (new entry)
8 Mercedes E-class (new entry)
9 Lexus SC430 (10)
10 BMW X5 (new entry)