I'd usually say "Buy the DVD if you really love this show", particularly since in the extras the ASOS Brigade looked down on pirating anime, e.g. YouTube (then again, most of the stuff on there's illegal). Of course, it all depends on how much cash you have. If you're low, you can check out Hulu.com; it's free, has Japanese and English (the latter with subs), and it's perfectly legal. Higher quality than YouTube as well. I don't know if they have Haruhi on there, since it's only limited to the US, but it's worth a look all the same.