[Mnemosyne]

I nominate Lalia the Fat, Estella Bolger, Diamond of Long Cleeve, and Rosie Cotton.

ETA: It'd probably be possible to do a whole list of "no repeats," but only by including the entire Gamgee brood or other* characters in Appendix C about whom we know nothing but a name.

*Although since we have an Epilogue we know something about some of said brood; and in fact a number of them are predicted by Frodo in the actual text...