How much $ are you looking to spend? Are you trying to do a full 5.2?
Spend the majority of your $ on the Left/Right mains and/or the sub!
A lot of people like these smaller bookshelf speakers, but they tend to also use a sub-woofer to fill in the bass on the low end. That does make some sense, as you get more for your $ on a bookshelf vs. the "equivalent" tower speaker, then you let your sub do the heavy lifting.
I also personally prefer towers to bookshelf speakers, and may even add a sub too! But, I have both configurations and there are merits to each.
For towers, start looking at the Pioneers (designed by Andrew Jones), or some of the offerings from Monoprice.com or the Dayton Audio speakers from parts-express.com.
If you are considering the sub + bookshelf route, start with the 12" sub from Dayton Audio/PE. You can also look at the Pioneer Bookshelf speakers or the dayton or monoprice. There are some Sony speakers on sale right now for around $90 that are supposed to be pretty good, but I haven't heard them and I personally tend to avoid Sony.
@zieglj01 is a pretty good resource for finding these good budget speakers for us!
NOTE-- You absolutely do NOT have to spend big $ to get very good sound. Spending the $ in the right place and at the right time is much more important than how much $ you spend.