I like a keyboard that offers a whole ton of features, something that's always important to me is volume controls, full media controls like play, pauses, as well as macro ability. If you want wireless head to the best wireless keyboard page.
The Logitech G510 is my current keyboard choice, although not a good budget build item, if you're a gamer this is worth looking into.
Logitech wins again with the Logitech MK200. Reliability, great reviews along with a mouse combo for a great price.
The most important thing for me is the placement of the computer keys, I don't like ergonomic keyboards, they just don't feel right, call me old fashioned. I also have to like the way the keys feel when pressed. I like a little resistance but a smooth key press. Pressing the keys needs to be relatively quiet, loud keys get old when typing pages for this website.
Last, I check features, I like media controls because I often listen to music while I'm on the computer. I'll pick a keyboard over key feel even if I have to give up some features. I'm not huge on all kinds of extra buttons or dials, but I must admit, volume is starting to become a must as well.