Template:U
[[User:{{{1}}}|{{{1}}}]]
This template is used as such: {{subst:U|Tmtoulouse}} which produces Tmtoulouse.
There is an optional second parameter that allows you to change the displayed name ({{subst:U|Bohdan|Sumtxt}} becomes Sumtxt).
This is an excellent template for the terminally lazy, since it saves at least seven keystrokes per use, or can make the difficulty of typing "unsigned" a distant memory.
Even shorter is [[User:example|]] (note the pipe "|" before the closing brackets), which gets automagically replaced by example.