The Old Blind Cat in Shinjuku has a long and fascinating history, as much as any jazz bar in town. It's located down in the second basement (B2) of a building right across from the East Exit of JR Shinjuku station, and dates to 1945 when it opened amidst the rough blackmarket that sprung up the day the war ended.
The bar passed through several owners' hands before the current owner Kikuchi-san acquired it in 1965. Longtime bartender Nishizaki-san ran the place while Kikuchi-san ran another joint over in the Shinjuku-San Chome neighborhood. (Nishizaki-san has been ill recently and is taking some time off; both these guys are in their mid-70s) During this time the OBC was a popular jazz bar amidst the chaotic Shinjuku streets of the 60s & 70s. World famous author Haruki Murakami even worked there briefly during his student days and loved it so much he opened his own jazz bar before focusing full time on writing.
The bar itself is old and charming, a railroad-car shape with a long counter bar along the left side, small booths along the right side. It's dark and there are no windows; this is not a bar for anyone even slightly claustrophobic or cannot be around second-hand smoke. The music is standard jazz though with a lot of contemporary live DVDs showing on the large TV hung above the bar. Last time I was there a Roy Hargove live set from Smalls in New York was playing.
The OBC is probably a bit heavy for casual jazz fans (B2, smoke, etc) but if you're a veteran jazz bar hunter then you will love it, as I do. See pics of OBC here at Tokyo Jazz Joints.
Use the East Exit or any of the Shinjuku subway exits in the map link above.