The first generation S40 was sold from 1995 through 1994. Like many other Volvos, it was only sold as a 4 door sedan and a station wagon. The standard engine was a 1.6 liter I4, while the top engine was a 2.0 liter turbocharged I4.
A diesel I4 engine was also available in some markets.
The first generation S40 was only sold with front wheel drive and, to the disappointment of many drivers, it was only sold with a 5 speed automatic transmission.
The second generation S40, sold since 2005, saw many improvements. The station wagon body style was gone, but a four wheel drive option was added to appease those looking for better performance. The top engine is now a 2.5 liter turbocharged I5. It is also sold with a turbocharged diesel I5 engine. The transmission options now include a 5 or 6 speed manual or a 5 speed geartronic.
The Volvo S40 PZEV is a partial zero emission version of this car that is sold in some states in the U.S. Volvo does not make nearly as much money on these cars, so they try to limit where they are sold to areas with stricter emissions standards. They include California, New York, Pennsylvania, New Jersey, Massachusetts, and Florida, along with a few others.
There are several places to find good deals on a decent used Volvo S40. The place I check first is the listings on eBay. There are also some original and aftermarket parts for sale on there.