Introductory:
These site provide a basic introduction to transgenderism
Alyson's Attic is just filled with introductory resources. Lots of little bits about almost everything. It's just like my attic!
"Gender Differences" is an introductory article written for an undergraduate psychology class.
GenderTalk is an real-audio radio program of "gender transgression at its best."
GENDYS Network Journal is an on-line journal with articles covering a wide range of transgender topics
Julie maintains Transgen, probably the most popular trans support mailing list ever!
Phil's site is informative and has an autobiography stressing the difference between sexuality and gender.
By Genre and in Numbers: is a collection of articles in english and french.

Gender-Queer Youth:
These pages help young transsexuals and young transgendered people.
Aunt Jenny is a wonderful grown-up transsexual women who has dedicated her time to providing a discussion group for young transsexuals. I haven't been on the list in several years (don't remind me how old I'm getting!), but I remember the list as middle and high school students. FtM and MtF transsexuals are both greatly involved members.
Evelyn is the mom of a MtF transsexual who transitioned when she was young. Evelyn wrote a book about her experience helping her child and she now provides it for free in English and Spanish on her web site. [Note: Evelyn's web site has been taken down for several months. I wrote her & she told me about her plans to have the book up for free. I'm putting the link here so you can keep checking back to see when she has it up.]
Julia: I hope Julia can be an inspiration to other teenagers because I'm very impressed with how self-assured she can be as a crossdresser.
Mermaids is an on-line and 'real-world' support group for the parents of transsexual children. It is located in the UK.
Yahoo's Transyouth club is another discussion group for trans-youth. I would guess most members are in high school and some are in college. Both FtM and MtF transsexuals are greatly involved.

Female to Male Transsexual and Transgendered Men: These site focus on issues concerning FtM people. Though I have a section specifically for FtM transsexuals, you will find many links to other trans-guys in other sections. I feel it's very important for all transsexuals, regardless of which 'direction', to share our experiences to help each of us grow.
Alex tinkers a lot in his garage; he even hosts a a real-audio program for transguys in there!
FTM Informational Network is a nicely designed general resource site for FtM transsexuals. It includes many essays and a mailing list.
FTM International is a comprehensive resource list for FtM transsexuals. The history section is particularly interesting.
Rory maintains another FtM mailing list
Stone Cowboy has collection of resources for the "Self-Made Man."

Family, Friends, & Significant Others: These sites try to help the people who are most important in the lives and transsexuals and other transgendered people.
Bess "want[s] to be visible as the significant other, wife, lover, partner of a Transguy, and as a woman who dares to define her sexuality in an order that denies her that right on every street corner." She says it so well I felt I had to quote her!
Loree & Marcelle : Loree is spouse of Marcelle, a trans-guy. Loree discusses what this means for her and her identity as a lesbian. They wrote many essays, one is also published in the book "Trans-forming Families."
Linda & Pat are two wonderful parents who "start[ed] out with a melancholy Catholic daughter and end up with a contented Jewish son." This is actually part of PFLAG dedicated to trans issues. But I personally would like to thank Pat and Linda for helping my parents when I came out!
Melissa & Kath's TeaTime Support Group: They wrote many essays about their lives as a couple with a crossdressing husband. Even some children wrote essays for this site!
Minnie is a prolific writer and the partner of a FtM transgender warrior (Leslie Feinberg).
Monique is a supportive spouse of a transsexual with lots of resources for significant others and family.
Joanna is the sister of a MtF transsexual. She wrote her personal story of dealing with her sibling's transition. And she wrote it honestly enough to share how confusing and complicated the whole experience was.