You can use almost every user control. All you need to do is uploading it to the /UserTemplates DocLib.

The best way to create a new user control is to use the SharePoint Designer, since most of the content will be out of SharePoint lists anyway.
In this chapter we create a list of download items.

1. Open your site in SharePoint Designer, select the /UserTemplates DocLib and open the WebLinks.ascx which is the user control that renders the top links on the right side.

2. As you can see we used the ContentByQueryWebPart. Alter ID and Title Parameter so they have a name that fits. Then change the ItemStyle too. We will need to add an XSL Template with the same style later. Save the file as FileLinks.ascx

3. Change to the design view and open the Web Part Properties. In Query section select the document library and change the Content Type to Document Library as well.

4. If you have additional columns in your document library, that you want to show in the control, go back to code view and write them to the CommonViewFields. Set it empty if not. For every field name, you have to add its type, separated by a coma. Divide fields by a semicolon. Remember not to put any spaces between. Otherwise the fields won't be available with the correct name.

5. Now go to the Style Library, select the document library XSL Style Sheets and open the BKSItemStyle.xsl.

6. Copy one of the templates and set the name to the ItemStyle you have specified in the second step. Don't forget to change the match clause. From here you are completely free to design the view of your list. Document Libraries have a Title and a LinkUrl Attribute. You won't need more for a simple download list.

7. Save the files and check them in.

8. Go to the /UserTemplates document library and give your created user control a title. Now it should be selectable in the UserControlZone's drop down list.