I've heard good things about Sea Foam, but decided to go with GM Top End Cleaner (only available through a GM dealer unfortunately). This stuff only goes though an intake (ie throttlebody) but not through gas/oil. Though it will mess up your oil so do this right before an oil change. The GM stuff "de-carbons" the internals of the engine, and I love it. Just did it to the Jeep, gonna do it to my WS6 in the spring! Comes in a can or as an aerosol. Don't think you'll go wrong with either product!
1995 Grand Cherokee Limited 5.2L V8, Quadra-trac - bought 11/21/03. Stock, but may change to get better mileage...
2000 Trans Am WS6 - not stock, and getting further every day...