Web Development
I have been an avid fan of RubyMine ever since I discovered it. I tried using other tools like Sublime Text 2, Textwrangler and others. The only other lasting editor I used was Vim on my Ubuntu Desktop and MacVim on my Mac.

There are tons of things I miss from Rubymine whenever I develop using other editors. Here are a few:
  1. Image Preview - Do you want to make sure you have the correct image to use in your CSS? Hover over the declaration and press Shift.
  2. Insane Code Inspection - Rubymine helps you be aware of deprecated methods, unneeded methods and overridden methods. 
  3. Checking of Source - A great feature I like about it is Command-clicking. Whenever I am not sure what a method does, I Command-click the method and I am instantly forwarded to the method declaration. This is quite handy if you want to check gem sources.
Here are a few shortcuts I have been using with Rubymine in the span of a year I have been using it. I really hope this helps Rubymine users like myself to ease up development and trim development time.

Joining lines (Shift + Ctrl + J)

I never had the idea that there was such a function in editors. I discovered this when I thought of a way to join lines instead of doing a backspace on every line in a 100+ line file.

Toggle Comments (Command + /)

This will be very familiar since this is used  by Textmate and Sublime Text. It will comment depending on which type of file you have open.

Show / Hide Project Folder (Command + 1)

I work mostly on a small 13" laptop and I need all the space I can get. The project pane can easily be hidden so that I can use up the the full length of my small screen.