Web site Sullr provides reverse phone number lookups with an attractive AJAX interface and Google Maps mashup. Next time you get a call on your phone from an unrecognized number, enter in the number and see if Sullr can grab the listing. If you're on your cell phone, you can point your mobile browser to wap.sullr.com for a mobile version (though it was down when I tested it). Sullr supports reverse lookups in the US, Germany, France, Italy and Argentina, and currently only looks up listed landlines (like most reverse lookups). If you've got a different favorite reverse phone lookup resource, share it in the comments.
[AU - Sullr's not available to Australians, obviously. But we've included the story just out of tech interest.]