@Flagg:
Why doesn't Jinbe fit in with the rest of them again? He's not the kind to serve under anybody and he's more of a friend on the level of Rayleigh. If Jinbe was the kind of person to join a crew then he would've joined Whitebeard–somebody he is indebted to a lot more than Luffy--but he didn't. Him joining the Straw Hats just because Luffy and him are friends is nothing but wishful thinking.
I like Jinbe, and I hope we see a lot of him at Fishman Island, but he just doesn't belong on Luffy's ship as a permanent crew member.
I realize this was probably discussed into the ground before I registered here but I just don't see why he's a viable candidate.
This debate was fought mostly in volume 3 of this thread, if you're REALLY curious. I suppose the cliff notes of the argument would look something like this:
1. A fishman/merman is likely to join the crew at the end of FI.
2. Jinbe is an exception among his peers.
3. His strength/potential/reputation are properly tiered.
4. A last request from Ace, then being impressed enough with Luffy to put his life on the line for him.
5. Loss of warlord title, which is a serious change in career path.
6. High probability of a sad past flashback, with a legendary mentor figure.
There's probably more that I'm forgetting, but that should do. I can argue any one of those points individually. If you agree with all 6, then he should be a viable candidate. That doesn't mean he's a shoe in, but definitely a possibility.