If you want a really good software, I will recommend NetNanny. It gets best reviewes in most of online polls. However if you don't want to overpay then you could try K9 or PCWebControl, both stable and reliable.
I would personally recommend getting Spector Pro, works great on both Windows and Mac. Here you will be able to find some more details reviews:
Hi, Tomas :) Well known fact that teens a are easily subjected to bad reputation sites, different attacks, spy and malware, It's not a secret, my young daughter also was victim of such sites in internet. Since then I decided to track her internet activity by means a parental control software based on keylogger principle, recently I've found a good source www.refog.com to download this soft and use it now. I’m confident in my daughter protection today, and can recommend you use this software with pleasure.
I also was looking for a good parental control program for a long time. There are a lot of them nowadays and it is very hasd to choose. I tried http://www.refog.com/ and was satisfied by its work. It helps to limit the usage of websites and to check the list of activities. Very simple and effective in usage.