Xfce

"Xfce is a lightweight desktop environment for UNIX-like operating systems. It aims to be fast and low on system resources, while still being visually appealing and user friendly." -from xfce website

Installation
Install the complete xfce desktop.

Or you can select only needed packages.

Terminal emulator
You may need terminal emulator for Xfce

Autostart
To start xfce automatically with startx.

Volume keys
With xfce4-volumed daemon.

Lightweight method using alsa.

Consistent gtk3 theme
Greybird theme has support for GTK2, GTK3, xfwm4, emerald and metacity.

Go to xfce menu -> Settings -> Appearance. Or run xfce4-appearance-settings. Select "Greybird" from the "Style" list.

Now GTK2 and GTK3 applications should have consistent look.

Additional applications
Application finder:

Volume control:

Text editor:

Removable media and drives manager:

Previewer for files from Thunar:

CD burning application:

Archive manager:

Plugin for Thunar for work with archives, uses or :

is perfect for laptop users. It displays battery percentage, time remaining, power source (AC or battery), fan status, warnings, and can even be configured to execute commands at certain power levels. This feature can be used to put the laptop into hibernate mode when the battery is almost exhausted.

is a small command line embedded into the panel. It's quicker than opening up another terminal when you want to run a command.

gives you a handy method of mounting devices listed in /etc/fstab just by clicking your mouse.

lets you monitor your hardware sensors, such as CPU temperature, fan RPM, hard drive temp, motherboard voltage, and more.

adds several window manager themes.

is a simple, handy calendar.

is an application to monitor and manage power usage. This is especially important for laptops! The power manager allows you to adjust screen brightness, choose maximum performance or battery-saving modes, and setup hibernate, suspend, and shutdown actions when the lid is shut or buttons are pressed. You can set xfce4-power-manager to warn you when your battery reaches certain levels, or even turn off your machine. The application comes with a couple of helpful panel plugins to display battery/charging status, and a brightness control.