XMol is very intuitive with a minimal user interface.

Keyboard commands:

1. i (atom index)
2. s (atom symbol)
3. c (cell boundary)
4. b (bonds)
6. ctrl+{x,y,z}: (view)
7. ctrl+{a,s,f}: (windows)
8. esc: (reset view)

Mouse behavior:

1. wheel up/down (zoom)
2. right click: (select)
3. left click: (pie menu)