Busted Halo
Sponsored by the Paulists and written by young adults for young adults. Includes discussion boards on various topics, a Flash trivia quiz, guides for seekers.
http://www.bustedhalo.com/index2.htm

Listening to God in Prayer
Booklet by a Filipino Opus Dei priest teaches a simple way of prayer as a conversation with God.
http://www.geocities.com/frjuliop/

Pray with the Heart
Litanies, novenas, the Way of the Cross, and other Catholic prayers.
http://prayers.pray-with-the-heart.org/

Awaken to Prayer: How to Pray As a Catholic
Includes history and practical advice. Draws on the riches of (Eastern) Orthodox as well as (Western) Catholic spirituality.
http://landru.i-link-2.net/shnyves/prayer.html

A Cry of Love
A meditation on the Passion, told in the first person.
http://digilander.libero.it/rexur/inglese/index.htm

Invisible Monastery
International, multilingual online group of Catholics who believe in the power of prayer, and who commit to praying weekly for each other's special intentions.
http://digilander.libero.it/monast/inglese/index.htm

Daily Virtual Retreat
One-way (read only) electronic mailing list. With different themes for each month. Short Scripture quotes and comments provide food for further meditation for each day.
http://ihrc.net/retreat.htm

The Spiritual Exercises of St. Ignatius of Loyola
A classic. The Ignatian method of prayer uses visual imagination to draw nearer to God. Intended for spiritual directors or retreat masters, but "directees" can benefit from this book as well.
http://www.ccel.org/ccel/ignatius/exercises.html

Between the Clouds
This (31 Day / Complimentary) "Rudder" attempts to weave the Christian contemplative tradition seamlessly with developmental psychology, anthropology and physics.
http://www.contemplativerudder.com

The Nine Ways of Prayer of St. Dominic
Many of these famous "ways" of prayer have to do with posture, using our bodies in prayer.
http://www.domcentral.org/trad/domdocs/0005.htm