Any and all 18+ panels, for sure. I've yet to attend one that wasn't worth it...except the 4chan panel at Sakuracon year before last, but that's an exception because the people running it had NO idea what they were doing.
The Anime Hunters panel is always a must. I feel bad for missing them at Sakuracon, but hey...major conflicts happen.
Speed Dating is always fun. Last year I got to play E-Card against all the girls I talked to (I was cosplaying Kaiji). In the end, when they ran out of girls, I ended up in a bizarre debate with a random guy over whether Norway or Iceland was more awesome (I argued in favor of Iceland). All in all, good times.
If there's a Fanboy/Fangirl Anonymous panel or something of a similar nature, that'll be on my list. The two I've been to have been great.
I'll definitely stop by the Ouran Host Club tea party. It's been a fun distraction the last two years, and it's a good way to meet people.
Anime That Scarred Me For Life is another obvious choice. My friends and I actually ran this panel at MewCon. I've been a big fan since the beginning.
Probably the AMV Contest, unless something adequately compelling drags me from it, as has been the case the last two years. Always a good way to see awesome AMVs you can't easily find online.
Probably the charity auction, if I'm able to. Might be leaving too early on Monday though, so I don't know. They should definitely have the charity auction earlier in the con. Catch people when they've got money. Two charity auctions, one at the beginning and one at the end, would be even better.
Also an obvious, but necessary mention: The Exhibitor's Hall. I'm on a very specific and very serious mission to buy a good Horo figure this year. Of course, Type Moon, Touhou, and Persona merchandise shan't escape my grasp either...not that I'll realistically have luck finding much ;_;. Gah, there are so many other series I wish they made merchandise for...so sad. Oh well, at least I can do my obligatory manga stockpiling. Maybe I'll find a copy of Tezuka's Swallowing The Earth...one can hope.