While I'm proud of all my Wikipedia contributions — indeed, I do a lot of minor edits and clean-up work — these are some of the more visible things I've done, which I think have turned out well.

Articles edit

Data remanence
I rewrote much of this from scratch, merging in several other articles in the process. I feel that the resulting article is a much better treatment of the subject, vs the scattered concepts we had before.
National Industrial Security Program
Created this, sourcing everything back to official documents, and addressing the DoD 5220.22M confusion.
Free On Board
Rewrote it from a confused mess full of redundancies and prescription, into a proper NPOV treatment of the differing meanings, with much better sourcing.
Software flow control
Rewrote it for style, adding structure and sections, content, clarification, table for reprsentation information. Still needs sourcing, though.
Acronym and initialism
While I haven't written much original content, I have done a lot of copy editing to organize the article and make it more useful to readers, and try and keep it NPOV. It still needs help, though. Especially that examples section!

Project edit

Template:Talkheader
This is a long-term project of mine. I've done quite a bit to add features to this template, making it (I hope) more useful and more flexible. I've tried to inject the spirit of NPOV into the discussions, as different people want very different things. My steady involvement there perhaps sometimes treads closely to WP:OWN, but I try to remain objective.
Wikipedia:Template messages/Cleanup
Organized the templates into sections by type, instead of having one massive list.
Wikipedia:Article message boxes
I contributed to the early discussion, invented the title and some of the other terminology, and wrote much of the docs.
Wikipedia:Citation needed
I tried to make this page more useful to the newcomer, by splitting up and giving more appropriate instructions. Minor, but key, I think, especially for such a visible page.
Wikipedia:Wikipedia in brief
Extensive copy editing and rewording; almost a rewrite. I like to think I've captured the major positive aspects of Wikipedia, rather than simply listing things Wikipedia is not.
Wikipedia:Alternative outlets
Merged redundant pages and created a "directory of alternatives" which is, hopefully, more useful to the newcomer.