For different color sets, also add one of these styles:
→ http://freestyler.ws/style/56882/wikipedia-dark-green-lustrous
→ http://freestyler.ws/style/57286/wikipedia-dark-blue-simple
→ http://freestyler.ws/style/58503/wikipedia-dark-gold-simple
→ http://freestyler.ws/style/57348/wikipedia-blue

Works on most Wikimedia sites, such as wikipedia.org, wikimedia.org, wiktionary.org, wikiquote.org, wikibooks.org, wikisource.org, wikinews.org, wikiversity.org and mediawiki.org

Latest changes:
2014-09-27 - minor fix for some search buttons.
2013-09-19 - fixed the new "VisualEditor", again.
2013-08-05 - fixed the new "VisualEditor".
2013-07-28 - fixed the new Table of Contents.
2013-05-31 - added wikivoyage.org domain.
2013-02-26 - fixed the crazy Wikipedia blunder they've made today with their updates; added wikidata.org domain.

You can also try some derivative works by other authors, which used this style as their base:

→ http://freestyler.ws/style/65605/clean-wiki (edited by Waschmittel@userstyles)

Table of Contents always expanded on the left, nice idea; search suggestions box slightly off position; style not compatible with my color sets :(

→ http://freestyler.ws/style/65976/wikipedia-clean-readable-smooth (edited by maximillan@userstyles)

interesting gray/lower contrast take on this; worth noting that the search is not removed, but only invisible until hovered(!); style not compatible with my color sets :(