There are many good websites. You should probably start with an unbiased explanation of ice ages at:
http://www.bbc.co.uk/weather/features/understanding/iceage_01.shtml
Yes, believe it or not, we are CURRENTLY in an ice age, in a small period of time called an "interglacial epoch" where glaciers have receded and things are a bit warmer.
We have been warming out of a major ice age glaciation from 10,000 years ago, and warming up from a "little ice age" going back several hundred years.
The odds we will head back to extensive glaciation, and the end of civilization as we know it, is quite high. That is why it was such a popular climate end-of-the-world scenario years ago, the geologic evidence is overwhelming.
(Unfortunately, you can't blame mankind for glaciations, so worry warts have to come up with something else.)
Other skeptical websites include:
http://www.skepticism.net/faq/environment/global_warming/index.html
http://mysite.verizon.net/mhieb/WVFossils/greenhouse_data.html
The site below explains the problem with accuracy and precision of experimental numbers in general, and an average global temperature in particular:
http://www.numberwatch.co.uk/Temperatures.htm
The main problem with blaming mankind for global warming, is that current climate is within normal variances seen in the past. So the contribution to current climate, if any, from mankind is not known.
The most abundant and important greenhouse gas is water vapor. This should be a positive feedback, and eventually evaporate the oceans, but it doesn't. Clouds reflect sunlight and provide a negative feedback.
When you discover that climate models don't model water vapor and clouds, you begin to look more closely at all the global warming claims a bit more skeptically, and eventually conclude they are for the most part complete nonsense.