Patients trust Google almost as much as their physician. (article) Not surprisingly, doctors too find the search giant results very useful.

Clinical Images
Google Image Search is very helpful when reading  "dry" subject from a book without illustrations. Check out the web page that Google shows below the image (when you click on it). Sometimes this can lead you to very interesting websites which are otherwise hidden on page 20-30 from the regular search results. We are all visual creatures and clinical images are definitely helpful.

Scholar Search
Google Scholar employs the same page rank algorithm used by Google to weigh the significance of a particular article. The problem with the Scholar is that it lags behind PubMed in updates. For example, if you search for a topic and the article was published several months ago, it will not appear in Scholar but it will show up in PubMed. Anyway, search for "scholar" and Google Scholar will be the first hit on both Yahoo and Google.

Use Medical Terms in the Search Query
Using "differential" or other medical terms to sort out the commercial websites is very useful. The other option is to go by the source, like "search term" + "NEJM", "AFP", "Merck manual", "eMedicine", etc., just like Kevin mentions it in his post. Google aslo offers personalized search that you can use to shift the slider to "Max" to leave the commercial websites out.

References:
More people consult Google over health - Times Online
How do I use Google? - Kevin MD
Some Great Google Tips - California Medicine Man
Clinical Cases & Images Blog