You have soft covers that typically roll-up. They range in price form $200-$500+. They are typically very durable, and very easy to work with. You can completely remove them with ease as well. Only downside is, they are not painted to match, and aren't really meant to be stylish.
Then you have covers like the undercover, a lightweight, hard cover. They are very durable, and can take a good bit of abuse. They usually cost in or around $500.
Finally you have hard tonneaus. These are by far, at least in my opinion, the best looking. These are the covers that are painted to match the truck, and usually have their own little design qwerks. These are the most heavy, and typically the most expensive. They range in price from $400-$1500+.
If you are looking for something to work with, and really like the painted hard tonneaus, I would recommend Gaylord's Butterfly cover:
http://gaylordslids.com/butterfly.php