There are many DNS services available. Most users are browsing the internet with default settings provided by ISP (internet service provider), so they're using the domain name systems provided by the ISP. Here come's the problem. These domain name systems might not work very fast, and they can be even not synchronized with some of the webpages on the internet, or they can even redirect some webpages (which is completely unpleasant).
There are a few DNS providers on the internet, that can offer you better internet experience than your ISP can. OpenDNS offers fast DNS services, for free or not, depending on the quality of services you want to have. If you make an account at OpenDNS (free), you can view detailed informations about what you're doing on the internet, and you can activate if you want, different filters, for blocking access to websites that contains pornography, hacking tutorials, mail services, messenger services, and many others. You can even have protection against phishing, botnet, and if you pay, against malware.
Google launched recently their own DNS services, and they actually offer the fastest internet on most of the regions on the globe. On my network (ClickNet Romania) they're the fastest. They're offering automatically protection against malware, but I don't know how efficient it is.
Now you probably want to know how to change domain name systems. If you're connected to the internet through a router or a modem, you should firstly try to change DNS addresses there (router/modem). If you connect to the internet directly (your computer makes the connection) or if your router or modem is set to bridge the connection or has automatically settings, try to change DNS addresses from your connection properties on your computer. Here is a guide from Google which will tell you how to do that: http://code.google.com/speed/public-dns/docs/using.html.
Official Google DNS site: http://code.google.com/speed/public-dns/
Official OpenDNS site: http://www.opendns.com/
Google DNS addresses are:
For any problems, you can leave a comment to this post.