When someone asks "What are good AdSense keywords?" they are really asking about the best keywords to optimize their pages with which have AdSense ads on them. Success with AdSense is all about driving traffic to niche websites. The chosen keywords to optimize the site's pages with will make or break efforts to earn income from Adsense.
Success requires choosing a niche area without too much competition. Yet, the niche must have enough interest to insure there are sufficient numbers of searches. Many people choose niches which are simply too competitive to ever have a chance of being ranked on the first page of search engine results. This is the most common mistake made when creating AdSense sites.
AdSense keywords for a given niche must allow the site owner to rank his or her pages on the first or second pages of Google and/or Yahoo search result pages. The best way to find these AdSense keywords is to brainstorm with the many free keyword tools available online. I have found even the free versions to be of great help for discovering AdSense keywords which can be used to optimize pages with. I particularly like the Google keyword tool. Simply do a search for "keyword tool" in Google and it is usually the first result.
When you find possible keywords, they should be checked in a Google search with quotes around them. Notice the number of total sites with that keyword in the content. For example, if there are 500,000 other sites with that keyword, it is probably too competitive of term for you to ever get traction with. On the other hand, if the AdSense keyword shows only 5,000 other sites, it can be very easy to rank well in the search engines.