There are a number of tools that can be used for studying the Gospel. The ones I find the most helpful are listed below:

Gospel Topics

Below is a short overview of the Gospel Topics section of the Church website.

BYU Speeches

Searchable collection of speeches delivered at Brigham Young University by Church leaders and others. Take a look at the quick intro to this great tool below:

Encyclopedia of Mormonism

Online access to the Encyclopedia of Mormonism. Here is a quick introduction to this excellent online tool:

LDS Scripture Citation Index

Complete index of all scripture passages used in general conference talks.

LDS General Conference Talks

All of the talks in different formats given from 1971 to the present.

Journal of Discourses

Easy to browse text format.