You were close, but you forgot -row:

use Tk;

my $top = new MainWindow();
my %density = (A=>1,B=>2,C=>3);
my $row = 0;
foreach (sort keys(%density)) {
    my $keytext = $top->Label(
        -height=>1,-width=>10,-text=>$_,-justify=>'left')->grid(-row=>
+$row,-column=>0);
    my $denbox = $top->Entry(
        -textvariable=>\$density{$_},-width=>5)->grid(-row=>$row,-colu
+mn=>1);
    $row++;
}

MainLoop();
[download]

1) You can use a Tk::LabEntry widget instead of separate Label and Entry widgets. The result is identical, but it's a bit shorter to code.
2) The -justify option controls justification when there is more than one line of text, which is not the case in your case. What you really need is the -anchor option and set it to 'w'.
3) To align all your text in the Label widgets, set the value of the -sticky option of grid() to 'ew' for each of your Label widgets.

HTH.

You can use a Tk::LabEntry widget instead of separate Label and Entry widgets. The result is identical, but it's a bit shorter to code.

This is not identical, because a LabEntry widget occupies only one cell, be it packed or gridded. This means that you can't easily align a number of vertically stacked LabEntries. (There are workarounds, but it's always easier to create Label and Entry seperately and use the grid geometry manager)

#!/usr/bin/perl -w

use strict;
use Tk;

my %density = (
  Some_Value    => qw(Something),
  Another_Value => qw(Something_Else),
  Some_More     => qw(Some_More),
);

my $mb = MainWindow->new();
$mb->minsize(qw(200 100));


for (sort keys(%density))
{
  my $keytext = $mb->Frame->pack(-side => 'top', -fill => 'none', -exp
+and => 1);
  $keytext -> Label(-text=>$_, -relief=>'ridge')->pack(-side=>'left', 
+-anchor=>'n');
  $keytext -> Label(-text=>"   ")->pack(-side=>'left', -anchor=>'n');
  $keytext->Entry(-textvariable => \$density{$_},-width => 15)->pack(-
+side=>'right', -anchor=>'n');;
}

MainLoop();
[download]

Thank you all for your help, I will definately use all or part of most of the responses here. I had another problem, and that is the fact that I have to display multiple columns of information. So I have a bunch of hashes that I need to display now. What I have done so far is to create frames and frames of frames, etc. Using this method, I can ->pack() everything in each frame. This is a little cumbersome, however, since I have about 12 frames now. Thanks again everyone.

See the RPN calculator tutorial on the Perl/Tk wiki for a worked example.

foreach (sort keys(%density)) {
    Tk::grid(
        $mb->Label(
            -text => $_,
            -anchor => "w",
        ),
        $mb->Entry(
            -textvariable => \$density{$_},
            -width => 5
        ),
        -sticky => "ew",
       );
}
[download]

Interestingly, what Tk::grid sees with the "procedural form" of call, is identical to invoking the grid method on the leftmost widget, and passing in the remaining widgets as parameters.

This is because a method call passes in the object as the first parameter.

--
I'm Not Just Another Perl Hacker