Google added some new features to drawings in Google Docs, choose 'Insert Drawing' in any document, spreadsheet, or presentation:

Custom shapes and lines, select 'Polyline' from the toolbar, choose shapes, fill them, and even move around points on a line by double-clicking the line.
Snap to Guides helps you align shapes with the canvas and with other shapes. This feature can be enabled by selecting 'Snap to Guides' from the edit menu.
Draw multiple lines let you quickly draw a sequence of related lines. Now when you finish drawing a line, arrow, or scribble, you stay in line drawing mode so you can start a new line immediately.