With Talika Gnome Panel Applet, you can get a Windows 7 like taskbar in Ubuntu. It is a lightweight alternative to the default window manager in Ubuntu and it supports window previews.
- 'Icons Only' Taskbar
- Window Previews
- Grouping of similar windows
- Show pin option for pinnable apps
- Supports pinning via drag and drop
- Option to show tasks from multiple monitors
- Option to close group with middle click
- Option to show preview on multiple windows only
- Pinining support for openoffice & some wine apps (like picasa)
- Choose custom icon for launcher
- Option to use monochrome icons
- Customizable icon sizes, space between icons and icon highlight color
Probably the most important feature about Talika is that it is really lightweight (6 mb in my case with 5 icons on applet) and would be ideal choice for low end machines.