[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. . . )