Glossary of Pali & Buddhist Terms
Glossary that covers many Pali words and technical Buddhist terms.
http://www.accesstoinsight.org/glossary.html

Buddhism Glossary
On the website of a university Buddhist study and practise group.
http://www.sinc.sunysb.edu/Clubs/buddhism/glossary.html

Buddhism A to Z
Compiled by Ron Epstein, Ph.D.
http://online.sfsu.edu/~rone/Buddhism/BuddhistDict/BDIntro.htm

Dukkha
An extensive discussion of "dukkha", a central term in Buddhism which is not directly translatable into English.
http://www.accesstoinsight.org/ptf/dukkha.html

Sesshin Glossary
Definitions of terms used at Zen retreats.
http://www.zenproject.faithweb.com/zen_teachings/sesshin_glossary.html

Glossary of Shin Buddhist Terms
Glossary of Shin Buddhist terms, from The Collected Works of Shinran.
http://www.shinranworks.com/readingtools/index.htm

Glossary of Zen Terms
A glossary of Zen as used by the Kwan Um School of Zen.
http://www.kwanumzen.org/misc/glossary.html

Zen Dictionary
A Japanese Zen dictionary of over 150 commonly used terms.
http://www.maximumbliss.com/zen%20dictionary.asp

Dharma Dictionary : Tibetan-English-Dictionary of Buddhist Teaching & Practice
An ongoing project involved in compiling Buddhist terminology and translation terms to bridge the Tibetan and English languages. Begun in 1979, it has slowly grown to a database of approx 5 megabytes with 65,000 entries.
http://www.diamondway-buddhism.org/diction/diction.htm