I found this list of RSS pheeds...I haven't tried them, so you'll need to experiment.

Usually you will need to use general keywords with RSS and can't get too specific. Any optimizing for long-tail keywords will need to be done on other parts of the page...

Substitute your keywords for key+word using this format:
las+vegas
pet+food

http://www.feedsfarm.com/s/key+words&format=rss
http://www.feedster.com/search/type/rss/category/blog/key+words
http://www.feedster.com/search/type/rss/category/news/key+words
http://www.feedster.com/search/type/rss/key+words
http://www.feedster.com/search/type/rss/category/podcast/key+words
http://www.findarticles.com/p/search?qf=all&tb=art&x=21&y=12&pi=rss&qt=key+words
http://rss.findory.com/rss/Blogs?q=key+words
http://rss.findory.com/rss/News?q=key+words
http://www.flickr.com/services/feeds/photos_public.gne?format=rss_200&tags=key+words
http://flickr.com/services/feeds/photos_public.gne?tags=golf&;format=rss_200
http://www.goarticles.com/cgi-bin/rss-search.cgi?search_content=key+words&l=20&s=1&c=none&D1=advanced
http://blogsearch.google.com/blogsearch_feeds?hl=en&q=key+words&ie=utf-8&num=10&output=rss
http://news.google.com/news?hl=en&ned=us&q=key+words&ie=UTF-8&output=rss
http://video.google.com/videofeed?type=search&num=20&output=rss&q=key+words
http://www.icerocket.com/search?tab=news&q=key+words&rss=1
http://www.icerocket.com/search?tab=blog&q=key+words&rss=1
http://www.icerocket.com/search?tab=web&rss=1&q=key+words
http://search.msn.com/news/results.aspx?q=key+words&format=rss&FORM=RSNR
http://search.msn.com/results.aspx?format=rss&FORM=RSRE&q=key+words
http://shopping.msn.com/xml/xmlresults/shp/?text=key+words,format=rss
http://ma.gnolia.com/rss/full/tags/key+words
http://www.podscope.com/rsssearch.php?s=d&assetID=&q=key+words
http://www.rawsugar.com/rss/search/key+words/
http://www.rocketnews.com/news/RocketinfoXML.jsp?must=key+words&age=0
http://www.rocketnews.com/news/RocketinfoXML.jsp?must=key+words&age=4
http://www.shadows.com/rss/tags/key+words
http://www.sphere.com/rss?q=key+words&datedrop=1&lang=en&x=0&y=0
http://feeds.technorati.com/feed/posts/tag/key+words
http://www.topix.net/rss/search/article?amp=xml&q=key+words
http://www.wired.com/support/search.html?query=key+words&src=wirednews&num=10&first=0&format=rss
http://answers.yahoo.com/rss/searchq?p=key+words
http://api.search.yahoo.com/ImageSearchService/rss/imageSearch.xml?appid=yahoosearchimagerss&query=key+words&adult_ok=1
http://news.search.yahoo.com/news/rss?p=key+words&sm=Yahoo%21+Search&toggle=1&cop=&ei=UTF-8&eo=UTF-8
http://api.search.yahoo.com/WebSearchService/rss/webSearch.xml?appid=yahoosearchwebrss&query=key+words
http://www.youtube.com/rss/tag/key+words.rss