Sumo

Videos:

• All top-tier (Makuuchi) matches with English commentary by NHK - youtube copy. ~~NHK posts a video with English language commentary after a delay of a day or two, it will be linked here when they do.~~
• Top 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 "11日目" or "5月21日"

More Info:

• all results from the JSA
• full schedule (without results) compiled by a fan site
• tournament leaders list 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!