MinchaTime.com - Have Mincha times emailed to you, or sent directly to your cellphone.
Tefillos.com - Full text of Parshas Hamon, Birchas Hamazon, Me'en Shalosh, Krias Shema, and Tefillas Ha'Sheloh
TefilaCards.com - Various tefillos typed and laminated on cards and sheets to improve the davening experience
PleaseDaven.com - Lists of people who need tefillos for recovery from illness, for parnassa, shidduchim, and other needs.
Beurei Hatefila Institute - Understanding the Words, Structure, and Development of the Siddur
Siddur Audio - Online resource for learning to chant the Hebrew liturgy of the siddur.
Kolatar.com - Find a list of cantors/chazzanim by Nusach, and listen to them perform.
IDaven.com - Online siddur easily accessible by Internet-capable handheld devices.
Minyan Minder - Allows a "minyan moderator" to coordinate attendance at a daily minyan
Tefilah Web - An online system to teach Jewish liturgical skills. Also has text of Shabbat services, Kaddish, and more.
Online Tefillos - Full text of Mincha, Maariv, Birchas Hamazon, Al Hamichya
How can we pray for someone else? by Rabbi Yitzchak Avraham Twersky
Tehilim Hotline - Submit names, and volunteers will recite Tehilim for them on a daily basis. Now you can also read tehillim online.
Chai Air Travel Tables - Calculate davening times for an overseas flight
Online Bentcher - Full text of Birchat Hamazon
Commentary on Shabbos Prayers
Live Western Wall camera at Aish HaTorah
The Davening Parrot
If you have any useful minyan links, or have written anything on your own about minyanim, let us know.