This is where I used to go back in my gakusei days:

Nonki (呑気). 1-20-6 Mukōgaoka, near Tōdaimae station. Tokyo's longest-running oden shop, founded in the Meiji era and still going strong. The centerpiece of the small shop is a giant cauldron full of boiling oden goodness. Order with the phrase tekitō-ni to let the chef decide, and figure on Y1000 for a serve and a beer to wash it down.

(courtesy Wikitravel Tokyo)

TokyoQ used to have a good review (which is how I first found it!), but it seems to have disappeared from the Net