Here are two nice little free apps that'll utilize your home/wallpaper screen. On the left (or the top, depending on your browser width) is Rich Olson's Wallpaper Labeler Free, which adds the text of your liking (such as the "if found return to" example shown) to the wallpaper of your liking — just as long as it isn't one of the iPhone's "built-in" papers. (Don't fret; the Free version has five papers, or lets you pick a photo from your album. If you spring for the US$0.99 version, the number of included wallpapers jumps to 27 — but buy now before the price jumps back to US$1.99!)
(Also from the same author: a US$0.99 app that creates LOLcats! We like this guy already…)
Back to matters wallpaper-ish. Respiratory Data Solutions LLC (whew, we're out of breath just saying that!) goes one step further with gCalWall Lite, which polls your Google Calendar and displays your next five appointments on a plain black background. (The programmer apologizes profusely for this, explaining that "Apple has not allowed [automatic wallpaper setting] in the SDK and until they permit it I cannot do it.") Also, it won't work unless you have Google Calendars (duh!). The "heavy" version offers user-selectable images and the ability to retrieve up to three more weeks of data.