I have to say Extreme Burn, Universal Impression, Andrew Gerard's Self Lighting Matchbook from Lit, and eXile were all winners for 2008 for me. If I had to narrow it down to one, I have to say Universal Impression wins trick of the year.
People should specify which Tagged. If you look at Ellusionist you can see that they are coming out with two "Tagged" which are completely different. Both of them are great, though.
For me it is thread, it's practical, has a fast set-up and once you're prepared you begin clean, end clean, and leave your audience wondering what the f*** just happened. So yeah thread is my favorite effect for 2008, It was really worth the price.