Here's what I feel is the easiest way: Click the trash icon in the dock. When the window opens, click and hold on the title bar trash icon until it turns black, and then drag it into the toolbar. BOOM done. Now you can trash files in majorly shorter dragging distances.
[Editor's note: I can't believe this hasn't been published here before; I wrote about it in the OS X Solutions Guidebook! So I'm listing it for completeness sake, and apolgies if it's a duplicate. Of course, you can also use "Customize Toolbar" to add a "Delete" button to the toolbar, and then you can delete files with no dragging at all.]

