Sumo

Videos:

• All top-tier (Makuuchi) matches with English commentary by NHK - youtube copy. ~~probably won't be posted til Monday. NHK posts a video with English language commentary after a delay of a day or so, it will be linked here when they do. I think you can watch it stream on their web site at various times per day - here's a schedule - and at some point they make it "video on demand".~~
• Best 10 bouts in the top tier (Makuuchi), with post-fight notes in English by Don Don
• All top tier bouts listed in Japanese with Japanese commentary by NHK: first half, second half
• Videos of the top ranks of the top tier listed in Japanese and without commentary, posted by the JSA - look for the ones that say "13日目" or "5月23日"

More Info:

• all results and standings by sumodb
• results and tier leaders from the JSA
• daily writeups in English by The Mainichi

Intro to Sumo

• introductory video
• more English-language intro videos at NHK's Sumopedia
• the wikipedia article has a lot of great information including on sumo terms.

SPOILERS IN COMMENTS OK!