Techron has a very strong following in lots of knowledgeable circles. It comes in both concentrated and not-concentrated versions, with not much differentiation on the cans, so be careful. One large can (for 20 gallon tank) of the concentrate will do good things to clean and keep clean. My mechanic also uses it as part of his standard 30k service.
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Mike Sullivan ('91 745 (171k), '93 965 (147k), '95 855T (60k), '98 V70XC (78k). Past Volvo's: '85 744 (256k), '86 245 (165k), '86 245 (195k), '88 745 (208k).

I was having some problems with rough idling immeadiatly after starting the engine. Used a product by STP (I think it was called Fuel System Cleaner) and the problem went away after one tank full of gas was consumed. I was very skeptical about using an injector cleaner, but thought I'd give it a try before I took the car in for a more expensive service. I think the product cost me $5.00 at Autozone.

BG-44k available at most autoparts stores. $20 a can, but from what I have been told, the reason it is expensive is because the stuff really works. Use it only once a year.