Just one short note on 42a - pay careful attention to the Bach's amendment of "Nechasim elu" to read "Nechasai." When you get to the end of the discussion on 42b, you'll see that his amendment makes the whole discussion read more clearly. Without it, the whole discussion is superfluous.
46b - Note the Rosh (I am referring to his second edition on "Taska", rendering it "Piska") vs the Ran on the difference between Rav Nachman and Abayye. The Ran's odd edition "beitzim" gives him a whole different way to look at the difference, but his approach has the force of logic behind it. It's hard to understand distinguishing between percentages, but it's easy to see a distinction between bathhouse commissions and a separate (egg) concession.
Of course, the gemara on 46b about splitting a shul - and the fact that individuals don't have that right - is also fascinating. It reminds of the Mishneh Berurah's forceful language regarding breakaways, in 150:2.
47a-b - The Raavad on the Rambam Hilchos Nedarim 5:16 is fascinating, with many ramifications.
On 48b we discuss avurei achsanta, warping the normal order of inheritance because of children's behavior. Of course, one must see Bava Basra 133b on this issue, and whether or not it is a good idea. Caren wrote her third-year law paper on this issue, and the way it plays out in halachic estate planning.
Also on 48b, we discuss kinyan sudar, and what works and does not work. This is a fascinating issue, and it comes up every year when we delegate people to sell chametz on our behalf. Whose pen do we use, and what if the delegator decides to walk off with it? See especially the Ran's concluding comments, which appear on 49a. See also Choshen Mishpat 195:3 for a ruling on this issue.
49-50 is just packed, wall to wall, with fascinating material (most of which has very little to do, directly, with Nedarim...)!
The issue of digestion and diet (on the figs at the bottom of 49a) is part of the foundation of the Rambam's dietary advice in Hilchos Deios as well as his "Medical Aphorisms." We ran a program on his dietary advice in the winter of 06/07, and it was a great hit. It's interesting to see the way the Rambam blends the gemara's advice with that of Galen and Arab writers, as well as eastern medicine. All are referenced in his writing, although he is explicit about the Greek and Arab sources and not explicit about the Eastern element.
The Bavel/Eretz Yisrael 'rivalry' shows up on 49b in comments about diet, reflecting a much larger issue which surfaces in other comments, such as the classic "Bavlai Tipshai" lines. You might look at some of my references here.
The unisex garment at the bottom of 49b is also interesting, in light of concerns for Beged Ishah. There is a major machlokes as to why the Torah prohibits Beged Ishah, and it has a practical ramification. Most rishonim believe it's because of the danger of inappropriate gender mixing, but the Rambam also notes a concern for the practice of idolatrous priests, who might wear a single garment from the opposite gender in their worship. If we follow the Rambam, then even wearing one garment from the opposite gender should be prohibited - so how do we understand this robe? Perhaps (and I admit that I haven't looked into it) the Rambam accepts the idea of a unisex garment.
The Yerushalayim shel Zahav that R' Akiva wishes to give Rachel on 50a is very interesting; recall the Gemara in Shabbos about going out with such an ornament on Shabbos, but more important is the Gemara in Gittin (7a) about wearing ornamentation after the churban. See the Hagahot Oshri to the Rosh in Shabbos 6:4; he permits this ornament post-Churban other than for weddings.
Also see the Ran (printed on 50b) on the legitimacy of annulling Kalba Savua's neder.