Actually there are several good Catechism texts in use in the various jurisdictions. Your local Orthodox Priest can refer you to one to use in your studies. Some of the ones that I have read that are both readable and have recommended to catechumen I direct in my parish are as follows (Please note some of the descriptions come from various publishing houses selling the the books) others are mine:
1) Eastern Orthodoxy: A Way of Life
by Anthony M. Coniaris. This book is highly recommended by Patriarch Athenagoras I as a spiritual milestone! Acclaimed by Dr. Nicholas Zernov, Archbishop Iakovos and numerous other Orthodox clergy and lay people as a simple book for the layman that makes the teachings of the Orthodox Church personal and practical. This book provides information on basic orthodox teachings, monasticism, marriage, Sacraments and Orthodox Theology.
2)The Law of God
by Fr. Seraphim Sloboskoy
Perhaps my favorite book about Orthodox Life and the only comprehensive treatment of the Orthodox Faith for the layman in English, Fr. Seraphim's work begins with Creation, Church History, and ranges through many of the predicaments of modern life in the Faith. It is a useful tool for catechesis, for individual pondering, and should certainly be found in every Orthodox home. Its only drawback is that it is written by a Russian Orthodox Christian and thus leans more to Slavic practice and not the Byzantine practices of the Antiochian Church I am affizited with, still it is an excellent book I used with my family of 5 children when we entyered the church.
3. A Catechetical Handbook of the Eastern Orthodox Church
by Dr. Diomidis H. Stamatis . This is a comprehensive Catechism by a noted Orthodox Scholar that I can highly recommended. It goes more deeply into Orthodox Theology beyond general lay levels of Bishop Kallistos Ware. The first part covers: What to Believe; The Existence of God; Incarnation; Redemption; Resurrection; Ascension; Judgment; The Holy Spirit; The Church and the Fathers; Remission of Sins; The End of Man. Part two covers: What To Do for Our Salvation; How To Be Sanctified; Daily Prayers; Spiritual Helps; Prayer and Worship; Divine Liturgy; Miscellaneous Topics. Part three focuses on: The Veneration of Icons; St. Isaac on Fasting; St. Chrysostom on Homosexuality; The Panagia; Women in the Church; Deaconess in the Early Church; Life After Death; Memorials; Monasticism; Ecumenism etc. Includes a Synaxarion of Selected Saints, the Celebration Dates of Selected Saints Throughout the Year, a Glossary and Bibliography. 592 pages.
4. The Orthodox Church
and The Orthodox Way
by Bishop KALLISTOS (Ware). The Orthodox Church is a nice general overview of the Orthodox Church , a brief history , and introduction to the beliefs of the Church by the eminent Oxford University Professor and Bishop KALLISTOS ( Ware). The Orthodox Way is the next companion volume , it is an easy to read book that you can pick up and lay down without losing the thought. It is written clearly and simply with reference to both Eastern and Western Christian sources. It raises the basic issues of theology; God as hidden yet revealed; the problem of evil; the nature of salvation; the meaning of faith; prayer; death; and what lies beyond. It covers the belief, worship and life of the Orthodox Church.
5.A nice Catechism for families with small children is A VISUAL CATECHISM OF THE ORTHODOX CHURCH.
By Metropolitan Hierotheos of Nafpaktos, illustrated by Yannis Yeremtzes. A catechism for all ages with beautiful iconographic-type illustrations in full color of the Symbol of Faith and many aspects of the Church and Christian life, briefly explained. it is short at 98pp
Well as you can see there is a great deal of Variety out there and there is one that will touch your heart and meet your needs in educating you in the Orthodox Faith. There are also several good OCA catechisms that are based on topics the Rainbow Series is available on the web at www.oca.org
as well as several topical catechisms they have put out and are available through St Vladimir's press I believe.