- Notepad++. I like it because its snappy and an outright replaced to notepad on Windows systems. It also have a bunch of plugins for everything. My favorite use of Notepad++ is to view and format JSON, It's also a pretty capable source code editor with line numbers and color highlighting for a lot of languages.
- Brakets. This free code editor is geared towards JS and HTML5 scripters - frontend people; it has this cool feature called "live html" where you connect Brackets to a live server and "edit" the site live. It also has a lot of plugins, I especially like the color/swatch plugin where when you edit CSS colors, it pops up a color selector helping you pick the right shade of blue or whatever. It's also nice that it understands CSS dialects like Less and SaSS.
- Lighttable. Although its sort of still in the dev stages it's quite stable on my ElementaryOS machine. It HAS GOT TO BE the coolest IDE I've seen and use. Lighttable has this killer feature where it cross a REPL with a source editor giving you the feel that you are editing running code. It also has this notion that a file is not the smallest unit of organization but a function is. Did I mention that it's free?
- Netbeans 8. Aside from being free, Netbeans has got to have the some of the best toolsets for Java development found on a single IDE. It has wizards for all of Java world's coolest libraries like Hibernate, Spring and Swing. It also has killer support for web technologies like AngularJS, HTML5, Less and SaSS. Aside from that, Netbeans also has built in support of workflow units like Maven, Git and Mercurial. It also has a pretty lively plugin ecosystem making able to support other languages not just Java like Ruby with Rails.