Basics: Main varietal: Garnacha / Tempranillo Main regions: Rioja, Ribera del Duero, etc. Personally, I'm a huge fan of Garnachas. If you are and would take a recommendation, Atteca is a great one. 100% garnacha. Muga is a good choice as well. Can't go wrong with either.
Spain has many good wine regions and sherry is unique and arguably the finest Spanish wine. Reds are most reliable from the Rioja and Ribera del Duero and whites from the Rias Baixas. Two other areas which are great scenically and with interesting wines are the Bierzo region and the Ribera Sacra both in the cooler north west, neither has any big producers like the more famous regions. Navarra wines are also very good value for money with a climate and soil similar to Rioja (it is next door) but without the name. If you want a really authoritative answer ask the question on http://www.wine-pages.com/cgi-bin2/ultimatebb.cgi