The Maintenance Mode plugin works great. We tried a couple of other underconstruction plugins, and to date we have found this one the easiest and most reliable to implement.
If you want to do some simple modifications, that is easily accomplished by going into the file maintenance-mode_theme_default.php (which you can open up with any web editor such as dreamweaver, or an ftp program such as Cute FTP using its built in edit function when you are viewing your files in your host via your ftp program).
We put up a simple modification at our site https://www.maxcomfinance.com where we changed some font colors, added some keywords, etc. It took no more then a couple of minutes to add the CSS which you can see if you right click on your browser and view the source code.
Probably you could add backgrounds but we did not feel it necessary.
Anyways we give Maintenance Mode by Michael Worhrer a thumbs up.
