How do I correlate /dev/sd devices to the hardware they represent?

You can look in /sys/block:

-bash-3.2$ ls -ld /sys/block/sd*/device
lrwxrwxrwx 1 root root 0 Jun  8 21:09 /sys/block/sda/device -> ../../devices/pci0000:00/0000:00:1f.2/host0/target0:0:0/0:0:0:0
lrwxrwxrwx 1 root root 0 Jun  8 21:10 /sys/block/sdb/device -> ../../devices/pci0000:00/0000:00:1f.2/host1/target1:0:0/1:0:0:0
lrwxrwxrwx 1 root root 0 Jun  8 21:10 /sys/block/sdc/device -> ../../devices/pci0000:00/0000:00:1f.2/host2/target2:0:0/2:0:0:0
lrwxrwxrwx 1 root root 0 Jun  8 21:10 /sys/block/sdd/device -> ../../devices/pci0000:00/0000:00:1f.2/host3/target3:0:0/3:0:0:0

Or if you don't have /sys, you can look at /proc/scsi/scsi:

-bash-3.2$ cat /proc/scsi/scsi 
Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
  Vendor: ATA      Model: ST31000340AS     Rev: SD1A
  Type:   Direct-Access                    ANSI SCSI revision: 05
Host: scsi1 Channel: 00 Id: 00 Lun: 00
  Vendor: ATA      Model: ST31000340AS     Rev: SD1A
  Type:   Direct-Access                    ANSI SCSI revision: 05
Host: scsi2 Channel: 00 Id: 00 Lun: 00
  Vendor: ATA      Model: ST31000340AS     Rev: SD1A
  Type:   Direct-Access                    ANSI SCSI revision: 05
Host: scsi3 Channel: 00 Id: 00 Lun: 00
  Vendor: ATA      Model: ST31000340AS     Rev: SD1A
  Type:   Direct-Access                    ANSI SCSI revision: 05
Host: scsi4 Channel: 00 Id: 00 Lun: 00
  Vendor: PepperC  Model: Virtual Disc 1   Rev: 0.01
  Type:   CD-ROM                           ANSI SCSI revision: 03

hdparm -i /dev/sdb

That should give you the model and serial number of the drive.

As the inimitable Gilles mentioned in this answer of his, if your kernel uses udev you can use the udevadm command to interrogate a device:

udevadm info -n /dev/sda -a

(Sadly, in some cases [doubly sad is that it's true in this case for me] udev is not used and/or udevadm is not available.)