The legend that is Dr. Horrible’s Sing Along-Blog is now for sale on DVD (region free). If you missed it when it first appeared on the web, get it now. And make sure to check out the official website as well.
Just in case you may need further convincing; here are a few reviews that speak to how amazing this entire project was.
Review in which the DVD is lauded
Review in which the DVD is lauded although the reviewer is possibly suspect
Have fun. And, trust me, if you have anyone you are at a loss as to a gift this holiday season, this will fit the bill.