git-gui, the Motif (either retro awesome or ugly as a sin, depending on who you ask) tcl/tk gui, besides being pretty fast, can do that. I get side looks every time I commit something in the middle of a file without commiting the entire file.

Select a file by clicking it's name.

Select the lines, alternative click then "stage this hunk/line to commit".

You can also add/remove entire files from staging by clicking the file icons.