1) Attachment Icons for Gmail (Link)
Attachment Icons for Gmail is a very basic idea but very helpful. What this extension does is that it changes the paperclip icon in Gmail (that stands for attachment) to a picture of what the attachment really is. For example if an email has a pdf attachment the icon is the not paper clip but the icon for pdf. I it does not recognize the file it will default back to the paper clip icon.
2) App Launcher Customizer for Google (Link)
App Launcher Customizer allows you to customize your Google Apps menu so that only the apps you want appear in the menu. You can add or remove any apps you need to.
3) Momentum (Link)
Momentum is a simple extension that creates an eye pleasing image when you open a new tab instead of the default "New Tab" screen.
Along with a new image, Momentum gives you the current time and your local weather.