1. Using the menu do a File > Find or via the keyboard Command-F
2. Set your search criteria
   Search in Home
   Name contains .Trash
   Visibility invisible items
3. Drag and drop the .Trash folder shown in the results window to your sidebar
4. As an added bonus you can paste a custom icon onto your new .Trash folder using the File > Get Info command
   
   

Method 2: Use the Go Menu
Jeffrey Matt gets the credit for this one!

1. Use Command-Shift-G or the Go To Folder command from the Go menu.
2. Type in ~/.Trash
3. The finder window pops up with the .Trash folder.
4. Drag and drop the .Trash icon from the top of the window to your sidebar.

Don't Do This
While it's tempting to use the File > Get Info command to remove the period from .Trash or rename it something else it's best to leave it as is. At very least when you reboot it will turn into just another folder, at worst you could mess up your operating system which is never fun.