Peripherals

As for the mouse, keyboard and speakers, I would tend to recommend a brand name product because they seem to last a little bit better. If you wanted to go wireless, don't cheap out. Cheap wireless can be very fickle to get working correctly and can become very aggravating. Other than that, simply pick a well reviewed item that fits your price range and looks ergonomically comfortable.

Final Check

Before purchasing everything for your computer it's important to make sure you have all the connectors you need. Usually a power supply will list the number of connectors is has in its specifications. Make sure that there are at least enough to power all of your devices. If not, power splitters and adapters can be purchased cheaply. In addition, make sure you have enough data cables to connect all your drives. Usually motherboards come with the cables you need, but it's a good idea to check.