Hello. I don't know if someone else already said this, but it seems not, so I want to explain how to add the border selection to the drag-left-button action. I find really useful for my modeling process.
With this settings you'll be able to do border selection dragging left mous button, to add selection with shift key and to subtract selection with alt key.
Let's see how.
1) First of all, we need to change the set-cursor shortcut. Open user preferences, go to input tab and set the item as in the picture. This way you have to press ctrl-alt-LMB to move the 3d cursor.
2) Now go down until you find Border Select. Open the item and copy the string view3D.select_border (see picture)
3) Go to the end of the 3D view(global) list (be sure it's 3D view(global)). Press the Add New button 3 times to create 3 new items. In each of them paste the previous string as in the picture. Then set all their options exactly as shown in the picture.