This page spun-out originally from http://expressionengine.com/forums/viewthread/92808/
A list of developers and sites that are offering add-ons.
http://www.solspace.com
http://leevigraham.com/
http://docs.markhuot.com/
http://www.masugadesign.com/the-lab/
http://www.designchuchi.ch/index.php/blog/category/expressionengine/
http://www.lars-kirchhoff.de/go/journal/section/Expression Engine/
http://brandon-kelly.com/apps/
http://eetemplates.com
http://lincolnite.com/ee/repeet/
http://www.putyourlightson.net/
http://www.brandnewbox.co.uk/products/
http://utilitees.silenz.org/index.php
http://media-cow.com/index.php/downloads/
http://www.lumis.com/site/page/imgsizer/
http://loweblog.com/freelance/
http://studio625.com/ee/
http://ryanirelan.com/utilities
http://www.ennovy.org/weblog/comments/the_livejournal_crosspost_module_extension/
http://code.google.com/p/shapeshed-ee-addons/
http://www.ngenworks.com/software/ee/structure/
http://natural-logic.com/software/
http://begoodnotbad.com/ee/admin-comments
http://www.vayadesign.net/blog/C11/
http://www.glenswinfield.co.uk/activity/comment/expressionengine_text_plugin
http://stevepsharpe.com/blog/permalink/ee-timesince-plugin/
http://www.hopstudios.com/software/
http://michaelbystrom.com/download/ee/
http://expressionengine.com/forums/member/33000/
http://expressionengine.com/forums/member/38398/
http://chrismacpherson.com/
http://nathanpitman.com/category/expressionengine/
http://www.purple-dogfish.co.uk/free-stuff/
http://www.hccdevelopment.com/Web-Based-Software/Products/
http://laxa.ca/ee_home.html
http://www.bridgingunit.com/labs/expressionengine/
http://www.caleydon.com/referencie/expressionengine/
http://www.tomkiss.net/ee/
http://www.twomile.com/services/detail/cms-add-ons/
http://barrettnewton.com/docs/
http://www.intoeetive.com/index.php/site/C1
http://webunder.com.au/weblog/category/expressionengine/
http://www.nikhedonia.com/notebook/category/expression-engine/
http://www.experienceinternet.co.uk/resources/
http://www.brianlitzinger.com/ee/
http://colly.com/s/774/
http://www.aviblock.com/blog/tag/add-on/
http://natural-logic.com/software/
See also addons hosted over at GitHub
Here are some from there
http://github.com/leevigraham
http://github.com/newism
http://github.com/MeanStudios
http://github.com/imagehat
http://github.com/amphibian
http://github.com/matthewpennell
http://github.com/smallbeer
http://github.com/slimkiwi
http://github.com/vinnyio
http://github.com/pkriete
Beyond this page, the other Wiki pages dedicated to Modules, Extensions and Plugins, and the official EE list, take a look at Devot-ee
Category:Add-Ons - Category:Plugins - Category:Extensions - Category:Modules