For keyboard/mouse you can not go wrong with Logitech. The Logitech optical mouse can be found for about $20 at just abnout any electronic store. I have the Logitech cordless keyboard, that I got at BestBuy for $40. I couldnt be happier with it. Its quiet, one less cord on the desk, and it feels good. I would recommend going to a store like Bestbuy where they have alot of keyboards on display. Type things on them to decide which one feels the best to you.
The Logitech Z-560s are excellent speakers. If your looking for something reasonably priced those are the ones to go with. If you want something cheaper, a set of 4.1 Creatives will run you about $50. If you need something high-end, Klipsch is the way to go (>$400.
HTH