Don't buy a premade computer if u want it to last as long as possible.
First go out and buy a nice case (at least a mid-tower) that u will be happy with for several years. (My computer case is almost 10 years old...plain black with no frills, but does the job)
Next, get the most powerful PSU u can afford. Try to get a 1000 watt one (or more). This way u will have power to spare as components requiring more power come along.
Buy a mainboard with the latest CPU compatibility. This way u can possibly later on upgrade your CPU if u want a better one.
Get a good, fast SATA6.0 type hard drive. 1Tb at least. It will probably last out 5 or 6 years at least. (I currently am running an old PATA 300Gb drive from 2002 and it works just fine for music storage and other things that don't require high bandwidth). So if u get the best drive today, it will still be useful maybe even 10 years from now. And of course u can add a new drive later too.
If u can afford it, get a bluray burner. They are all backward compatible with DVD and CD.
Keyboard and mouse don't matter so much as they haven't really changed hardly for nearly 20 years. (I actually still use an old clunky IBM, beat up, heavy as hell, keyboard that each key clicks when u press it. The thing has survived things these new flimsy keyboards would never make it through) The newer wireless ones are nice though.
Get a decent video card, but not the most expensive top of the line one. Those top of the line ones, usually go down by at least half when the next model is released. And by the time the newer model is released, all the bugs have been worked out of the older one. Video cards are one place it's not good to jump on the newest quick. Get the tried and true and it will cost u a lot less (and possibly save u a headache too).
Naturally u want all of these things to be standard. That way if u ever want to replace the mainboard for some reason, the rest of your components u can keep.