Simply the best subgenre of metal out there. Combines the distorted guitars and powerful drums of metal with the beautiful symphonic sound of classical orchestra instruments, such as violins, pianos, cellos, etc.
Some great symphonic metal bands include: Rhapsody of Fire, Therion, Symphony X, Nightwish, Kamelot, Angra, and more
The best kind of metal there is out there. It's got the hardcore drums and guitars of heavy metal, but most of the time beautiful symphonies (like in classical music) are added, mainly by instruments such as acoustic guitar, piano, keyboard, violin. In other words, a brilliant work of art.
Some good symphonic metal bands are Within Temptation, Epica, Delain, Nightwish, Otep, Leaves' Eyes, and Tristania.