Japanese drama shows

Ocassionally I'll pass by a station that shows a Japanese drama, samurai epic, or yakuza soap opera.  Since I have no idea what any are called, which ones or popular, or what are considered the best or classics, are there any recommendations or further information?

Yoo
I watched GTO / Gokusen I / Gokusen II /Densha Otoko
For fun I like Gokusen series but for romantic aspect I prefer Densha in my first list :-)