Before I came to live here, I would visit Japan every year and one of the places that was always on my visit list was Harajuku.
At the time, I came mainly to buy a load of idol booty - there are many shops selling photos of idols. Theres also a huge toy shop with seven (I think its seven) floors of toys called Kiddy Land. You'll also find that the whole town is flooded with school girls - if you like school girls (no matter what day of the week it is) then you know where to go ^^;
Harujuku is also the place where you can see many live bands playing in the streets - a tradition thats been going on for years.