Sitemaps:
Have you made a Google Site Map for your site? You can check out Google's Webmaster tools at https://www.google.com/webmasters/tools/docs/en/about.html or you can also use a free automated online sitemap generator such as: http://www.xml-sitemaps.com/ (and this site explains a lot more about the sitemaps http://www.auditmypc.com/free-sitemap-generator.asp). Then upload the file to your site, login to Google and submit the link to it. You can also do the same thing for Yahoo. These files help the crawler robots that visit your website by alerting them to all the pages on your site, the frequency that you update your site and other important information.
Banner Advertising:
I have found over time that banner advertising isn't as big of a bang for you buck for a small company as something like Google AdWords. The two positives of banner ads are that they may build brand recognition for you over time (people constantly seeing your company name/logo) and they can help direct potential customers right to a specific page on your site. The drawbacks are that a very small percentage of people actually click on the ads and they are usually costly (you can read a more in-depth article about that here: http://www.thomasclaburn.com/2002/06/the_banner_ad_is_dead_ok_not_r.html). If you do consider banner advertising, make sure the site you're advertising on gives you a way to view statistical information about clicks from your banner and find out whether they charge per-click (and if they do, if they have any contingencies for click fraud), per month, or in some other manner.