In case you’re missing Neil Patrick Harris while you await the next season of How I Met Your Mother, or in case you still hum the songs from Buffy‘s “Once More, With Feeling” episode, or in case our Firefly Fridays feature doesn’t provide your computer with your minimum weekly requirement of Nathan Fillion — you’ll be pleased to learn that Joss Whedon’s Web musical Dr. Horrible’s Sing-Along Blog finally has a premiere date. The 42-minute mini-musical about a lovelorn supervillain, much discussed here at PopWatch, will stream in three 14-minute installments, with the first debuting on July 15 and the others following on the 17th and 19th. They’ll stream for free through July 20 at drhorrible.com; after that, it’s not clear, though there may be a DVD in the future. (Hat tip to TV Guide‘s Matt Roush for the details.) Mark your calendars now for your appointment with the doctor.