ASUS Silent Series 9600GT
That's right, another silent ASUS card. As much as I like to diversify the recommendations I give out, in this case I simply could not justify any other card. There are very few passively cooled cards available that have the ability to play games at reasonably high detail and resolution settings. In fact, it seems that passively cooled gaming cards are, as a rule, a bad idea to buy. This ASUS is a rare exception, and that makes it a very good card.
As with all passive video cards, it is important to be reasonable with your expectations. The 9600GT will not play Crysis well with high detail setting on large monitors. However, it will play any Source engine game at high detail settings, as well as virtually any MMORPG or strategy game.
In terms of cooling, it is obvious why the ASUS's 9600GT manages to buck the trend of passively cooled gaming cards which overheat. It has a massive double-height cooler that spans the entire length of the 9600GT, which is about 8 inches long. Obviously, this is not a card that is going to fit into a slim HTPC, and if you're building an HTPC it is likely that a Radeon 4350 or 4670 will serve you better, depending on the level of performance you need. But if you for some reason need a gaming machine which is extremely quiet, then the ASUS Silent 9600GT is absolutely the card to buy.