Please Submit Your 5 Most Geschmack Sugyas in the Talmud

Ok, here's a twist. Lately, I've been inspired by a few of the jblogs out there, especially OnTheMainLine, Chardal and yes Happy , as well as some of Mis-nagid's and B Spinoza's comments (and, yes, even Gil, but not DovBear) to go back to some kind of regular learning.

I think all the blogging awakened that dialectic Jewish gene in me. I have also been exposed to how interesting some learning came be, in terms of the philosophical debates that ensue when you're "learning" with the right person. At the same time, I get tired of debating "theory" or "theology."

I also had a very interesting session of learning with a non-kiruv (as far as I know) Rabbi who is amazingly well-versed and yet at ease with a skeptical yet beginner level learner such as I.

We've gone through some great discussions about sugyas in Brachos. I want to take advantage of all of you in the Jblogosphere to point me in the direction of 5 of the most Geschmack Sugyas you can think of that you've learned and learned again.

I know, the purists will say, unlike Steinsaltz, there's no such thing as the "essential Talmud" it's ALL essential, and therefore, citing "favorites" misses the point. However, please indulge me. I expect that a compilation of great sugyas will inspire me to keep at it and will build a foundation in classic talmudic debates as well.

So, here goes format-wise:

1. Just list 1,2,3,4,5 with cites.
2. if you have more time, then please tell me why you like it so much.
3. I'm not looking for legal fundamentals, but rather the more philosophically relevant sugyas if that makes sense. It doesn't have to be aggada, naturally. The point is, don't assume that I'm unfamiliar with classic halachic passages and need to get "the basics" first. Rather, just tell me what you enjoy most and if it's halachic and basic, that's just fine.
4. If you believe in shar, then you will get a lot, as I intend, b'lie neder, to learn all of the sugyas submitted to me "inside." No promise of tosofos, akiva eiger, R Yonah, etc, but you can certainly take me through how commentaries play a role in what you like.

I actually asked Godol Hador to tell us BT's why learning was indispensable for him (he had said so in his "parting post" (there've been so many since then). But alas, he never got back to me.

Looking forward to hearing from you all.