[kamaal]

"wollw" and "DrJ" I am talking about command auto completion, not word auto completion inside the editor.

In emacs, for word auto completion M-/ is just too awesome.

[beaumartinez]

Pressing Tab completes commands in command-line mode, and its very smart. (Be sure to :set wildmenu to see a list of all matching commands as well.)

[super_mario]

Even without wildmenu option, repeatedly pressing TAB key will cycle through the list of matches.

[hesitz]

What's more, you can press <ctrl-D> to view the whole list of possible completions at one time. For example, enter ':colo ' then press <ctrl-D> and you'll see a list of all the colorscheme names. (The space in ':colo ' is important, since if you press ctl-D with just ':colo' Vim will just show you the 'colorscheme' completion. . . )

[Gonsalu]

You can press the tab key in Vim to get command auto completion.

For example, :colo<tab> completes to :colorscheme.

[wollw]

Command-line mode has tab completion. I'm not aware of there being auto completion in the other modes.