There's a lot of information out there about the Pagan "Wheel of the Year," and most of it is fairly redundant... and largely historically inaccurate. I don't vouch for any of this information. You can decide for yourself by reading many different explanations, but in the end, the Wheel is mythology that is meaningful to you. Write your own Great Story, as I did.
Here's a comprehensive collection of resources. Let me know if you have any I've missed.
Entire Web Sites:
Wheels of Specific Traditions:
Eclectic Collections:
Different Wheels
Rituals:
Other Writings:
Music and Lyrics:
Merchandise: