Cables and connectors
To avoid having unused cable to ensure an optimal airflow, it's best to go for a modular power supply. This is not a given in this 300-450 watt segment. Only five out of the 39 PSUs are modular: the Be Quiet! Pure Power L8 430W, the Cooler Master Silent Pro M2 420W, the Corsair CX430M 430W, the OCZ Silencer Mk III 400W and the Seasonic Platinum Series Fanless 400W. Modular PSUs aren't necessarily more expensive, as Corsair proves with the 50 euro CX430M.
The connectors vary widely in this segment, as you can see in the chart. Twelve power supplies (all 400 watts or more) have two PEG connectors, which is required for the more high-end graphics cards. A single 6-pin or 8-pin PEG connector is more common, and this is enough for powering a single mid-range graphics card. Four power supplies have no PEG connectors and therefore can't be used for a dedicated graphics card. These are the Be Quiet! System Power 7 300W, the FSP FSP300 and FSP350 and the Huntkey CP 350W.
The number of Serial ATA power connectors differs also. The most deluxe models have six and the Be Quiet! Straight Power E9 450W even 7. Four is typical, but some only have three or two. That's getting tight, if you want to hook up an SSD, HDD and optical drive than you'll need to get adapter cables first.
Something you also have to pay attention to is the length of the connector cables. If they're very short you could have a problem reaching all of the components, not to mention cable management. The Huntkey CP series have the shortest cables at 36 cm. All of this information is in the chart.