Ports and Connections
One of the features often neglected by buyers until after they've already made a purchase is the number of ports and connections available. These ports determine the types of devices that can be plugged in to the laptop, as well as their number.
Most laptops will come with at least two USB ports and a video output port of some type, as well as Ethernet and headphone and microphone jacks. If you are a basic user, this may be all that you really need. However, it's becoming increasingly easy to fill up a mere two USB ports. One external hard drive and one wireless mouse is all it takes.
Ideally, you should be looking for a laptop with three USB ports or more. At least one of those ports should be USB 3.0, the new high-speed version of the port which provides faster transfer speeds than previous incarnations.
I also suggest looking for a laptop with HDMI out. If you choose to hook up the laptop to an external display at any time, HDMI is by far the easiest way to do so. Virtually all modern displays are compatible with HDMI, and those few that only offer DVI can be used with HDMI via a simple adapter.
FireWire and eSATA ports are, at this point, considered legacy ports are rarely found in new laptops. This is because USB 3.0 is quicker than either, so device compatibility is the only reason to include them.
Some new laptops, like MacBooks, include a port called ThunderBolt. This is a high-speed port even quicker than USB 3.0 that can support both external displays and peripherals hard drives, though so far there aren't many products on the market that support it.