Google Maps offer a way of enhancing your listing with Google Tags.

While Google maintains this does NOT effect placing on Google maps, it certainly will make your listing, when it appears, pop. The easier you can make it for someone to click through to your website the better. You want to stand out among the Google Map listings and this will help.

The advertising fee is a flat $25.00/month. Nice to avoid the pay per click campaigns and the time spent analyzing the keywords for your website.

Read more here: http://www.google.com/help/tags/

Seems like one of the simpler advertising choices online.