How to set a Monospace Font for Dashboard Sticky Notes Widget?
This is possible, because widgets are HTML, CSS, and JavaScript based. Here's how:

First, go to /Library/Widgets and find the Stickies one. Copy it to ~/Library/Widgets and name it myStickies (or something else).
Close the Stickies widget in Dashboard.
Now, go to the myStickies.wdgt version you copied and right-click it. Choose Show Package Contents.
In the new window that appears, right-click on the Stickies.js file and open it with your favorite JavaScript editor (if you don't have one, TextWrangler is great and free).
Now, use the editor to find the line var fontArray = new Array; (should be around line 407). You'll see below that line a bunch of lines similar to each other, saying something like fontArray["font name"] = 1,. You want to copy the last one of those (American Typewriter), and paste it back below itself. Then, change it so it looks like this: fontArray["Courier New"] = 8;
Save and close this file.
Now, open (from the same folder) Stickies.html in an HTML editor (TextWrangler works).
Find the line that says, &lt;select id='font-popup' class='popup' onchange='fontchanged(this);'&gt; (should be about line 40).
Below that, you'll find a bunch of lines similar to each other, each beginning with &lt;option value. Copy the one for Gill Sans, and paste it below itself.
Edit it to say &lt;option value ="Courier New"&gt;Courier New&lt;/option&gt;.
Save and close this file.
Open Terminal and type killall Dock. This restarts Dashboard.
Now, double click the myStickies widget file you made. It will open in Dashboard. Follow the normal procedure of clicking the i and changing the font. You'll have a Courier option, and it will be that font. Yay!