Left to right:
A-RNA double helix

PDB: 1SDR NDB: ARL062
5'-r(UpApApGpGpApGpGpUpGpApU)-3'
H. Schindelin, ..., U. Heinemann, "Crystal Structure of an RNA Dodecamer Containing the Escherichia Coli Shine-Dalgarno Sequence," J Mol Biol 249, 595-603, 1995.

B-DNA double helix

PDB: 1D65 5'-(CpGpCpApApApTpTpTpGpCpG)-3'
K. J. Edwards, ..., S. Neidle, "Molecular Structure of the B-DNA Dodecamer (CGCAAATTTGCG)2; An Examination of Propeller Twist and Minor-Groove Water Structure at 2.2 Angstroms Resolution," J Mol Biol 226, 1161, 1992.

Z-DNA double helix

NDB: ZDJ050 5'-d(GpCpGpCpGpCpGpCpGpC)-3'
C. Ban, ... M. Sundaralingam, "Crystal Structure of the Self-Complementary 5'-Purine Start Decamer d(GCGCGCGCGC) in the Z-DNA Conformation - Part I," Biophysical J 71, 1215-1221, 1996
Warning: CHIME not making all bonds correctly!

Peptide Nucleic Acid double helix

PDB: 1PUP
H. Rasmussen, ..., P. E. Nielsen, "Crystal Structure of a Peptide Nucleic Acid (PNA) Duplex at 1.7 Angstroms Resolution," Nat Struct Biol 4, 98, 1997.