This page contains some interesting trivia facts for the series. Most of these trivia facts were obtained from the Erin Hunter chat transcripts, but some of them were things that I noticed myself. I will try to avoid spoilers as much as possible in these pages, but it is still quite likely that there will be some minor spoilers contained within the text. (Warrior names, cat's mates, etc.) I will do my best to avoid anything major though.
In early ideas for the warriors series, Bluestar was originally going to be named "Moonstone".
When Erin Hunter first started writing the warriors series, she only intended to make one book.
Heavystep, a Shadowclan elder, is mentioned as dying twice throughout the course of the series. Erin Hunter said that this was a mistake. Aparently, every time Heavystep died, Erin Hunter forgot to remove him from the characters list. Because of this, every time he died he would simply return in the next book as if nothing ever happened.
Erin Hunter revealed in an online chat that Scourge is Firepaw's half-brother. They both had the same father.
Rowanclaw, Tawnypelt's mate, started out as a she-cat and then changed genders so that he could father Tawnypelt's kits. Opps. =o
Brakenfur, Cinderpelt's brother, is the father of Cinderheart. (If you don't understand the significance of this, read Sunrise)
By the end of the third series, Thunderclan has kin in every known clan and tribe (Except possibly Skyclan). Power of Three Spoiler
If you have seen The Lion King click here for some other interesting trivia showing resemblances between warriors and The Lion King. (Warning, major spoilers for the Power of Three series and all previous books.)