Continuing the discussion started in the Apple II - Compact Flash thread, I thought I'd cover some of the other devices I've found in my wanderings.
DivIDE for ZX Spectrum
This provides an IDE interface for Compact Flash or PATA HDD or CD-ROMs. Multiple firmwares are available with different capabilities, but the default FATWare can access multiple FAT16 partitions on a device, and includes a handy menu for navigating drive contents.
I have one of these and it does everything it says on the box.
RWAP Software sell an enhanced version called the DivIDE+.
HxC Floppy emulator
This device can be plugged into a standard FM/MFM floppy interface to allow the use of SD cards for bulk storage. Works as a replacement for 8", 5.25", 3.5" and 3" drives on multiple systems including Atari ST, Amiga, Amstrad CPC, Spectrum +3, MSX2, Commodore 1581, TI 99/4A, TRS-80, Acorn/BBC, Kaypro and PC. Uses FAT32 partitions and has a built-in native application for some platforms including Amstrad CPC.
This looks like a great device and is likely to be a future purchase of mine.
CFFA 3000 for Apple II series
As mentioned in another thread this card allows the use of CF cards (and some other PATA devices) as well as USB sticks as storage for the Apple II series. As I understand it the CF/IDE interface appears like a Profile drive and is ProDOS formatted. A USB stick can hold multiple floppy disk images, and a button press lets you cycle between the disk images.
AtariMax MAxflash for Atari 8 bit computers
Available in multiple capacities these flash cartridges look just like a normal ROM cartridge for the Atari series. You can load muliple cartridge ROMs and select which one to run on boot. Can be programmed from an Atari or by PC using a USB programming kit. Not the cheapest solution I've seen, but very well designed.
SIO2SD for Atari 8 bit
The SIO2SD does exactly what it sounds like - it has an SIO socket on one side and an SD slot in the other, allowing an Atari 8 bit to use it just like a 1050 floppy drive. Accesses FAT12,16 and 32 partitions, but does not read SDHC cards.
SD2IEC for Commodore 64
There are many flash storage interfaces for the C64, such as the 1541 Ultimate and 1541-III, but the best of them seems to be the SD2IEC. Based on an Atmel ATmega644 microcontroller it is said to have the best performance of the lot. Can be bought built-up from NKC Electronics. This board emulates a 1541 disk drive and uses SD cards for bulk storage.