EDIT: Some of these styles have since been accepted into the Django repository. I'll leave this post up though since the process is still the same and you may have different ideas for your own styling.

Here's a small bit of CSS you can add to the bottom of Django's default admin CSS to make it a little nicer/user friendly. Place the file in your static directory like so: static/admin/css/base.css.

/* Place these styles at the bottom of the default Django admin styles
https://raw.github.com/django/django/master/django/contrib/admin/static/admin/css/base.css*/

@import url(http://fonts.googleapis.com/css?family=Open+Sans);
body{background:#fdfdfd;font-family:'Open Sans','Lucida Grande',Arial,sans-serif;}
#header{
    background: #fbfbfb; 
    background: linear-gradient(to bottom,  #fdfdfd 25%,#ececec 100%);
    border-bottom: 1px solid #b2b2b2;
}
#header, #branding h1{color:#181818;}
#header a:link, #header a:visited{text-decoration:none;color:#1B9EE0;}
#header a:hover{text-decoration:none;color:#0E8FCF;}
div.module{border-radius: 3px;}

ul.messagelist li {
    background: #dcffd5 url(../img/icon_success.gif) 5px .3em no-repeat;
}

ul.messagelist li.warning{
    background: #ffc url(../img/icon_alert.gif) 5px .3em no-repeat;
}

ul.messagelist li.error{
    background: #fff5f4 url(../img/icon_error.gif) 5px .3em no-repeat;
}

.errornote{
    border: 1px solid #dd2222;
    color: #dd1111;
    background: #fff5f4 url(../img/icon_error.gif) 5px .3em no-repeat;
}

ul.errorlist{
    border: 1px solid #cc1111;
    color: #ffffff;
    background: #dd1111 url(../img/icon_alert.gif) 5px .3em no-repeat;
}

ul.errorlist li{
    background: transparent;
    border: none;
    margin: 3px 0 0 0;
}

ul.errorlist li:first-child{
    margin-top: 0;
}

.errors, .form-row.errors{
    background: #fff5f4;
}

.errors input, .errors select, .errors textarea {
    border: 1px solid #dd1111;
}

Then add an admin/base_site.html file in your templates directory and paste in this, replacing the project name with your own.

{% extends "admin/base.html" %}
{% load i18n %}

{% block title %}{% trans 'Project Name Admin' %} | {{ title }}{% endblock %}

{% block branding %}
<h1 id="site-name"><a href="/admin">{% trans 'Project Name Admin' %}</a></h1>
{% endblock %}

{% block nav-global %}{% endblock %}