Google has a large collection of free fonts that are hosted for use on web sites. You can use them in your own personal CSS for this site if that's your kind of thing. Here is example CSS that you could paste into your Display Settings in the "On-Site CSS Markup" field. I think it looks good with the Dark theme selected, but it should work with any.

@import url('http://fonts.googleapis.com/css?family=PT+Mono');
@import url(http://fonts.googleapis.com/css?family=Merriweather:400,40
+0italic,700);
* { font-family: 'Merriweather', serif !important; }

.titlebar {  display:none; }    /* Remove title bar from top of every 
+screen */
.monktitlebar { font-size: 80%; }    /* Make top link list a little sm
+aller */
textarea { width: 90%; height: 30em; }   /* Don't post through a keyho
+le */
tbody.nodelet td { font-size: 14px !important; }   /* Reduce sidebar s
+quint */

/* Put border around code areas, and select  monospaced Google font */
tt.codetext {
    display: block;
    margin-right: 5px;
    padding: 4px 4px 4px 4px;
    font-size: 96%;
    border: 2px solid gray;
    -webkit-border-radius: 3px;
    -moz-border-radius: 3px;
    border-radius: 3px;
    font-family: 'PT Mono', monospace !important;
}
[download]

If you do decide to use different fonts, google makes it quite easy:

Find the font you like and click on its "Quick Use" button

Scroll down to step-3 for your selected font

Click on the "@import" tab (since Standard is shown by default)

Copy the shown "@import" line for your font

In Display Settings, replace the import from the CSS above to use yours instead

You'll also need to copy the font-family line from step-4 and replace it in the CSS too

Obligatory Screenshot and another Screenshot with Indie Flower font

*The code-border CSS was based on a PM post that evades my search fu right now, sorry