Here is a visual compilation of the Old Machinery blog posts about the Sinclair QL computer and some pointers to replacements.
1. Display: RGB TTL, RGB Scart, Composite Video, TV. Connecting to 1084S.
2. RWAP Keyboard membrane replacement
3. Extension slot: Tetroid Disk Interface or Gold Card (QubIDE interface, Memory/CPU expansions, Super Gold Card)
4. HxC Floppy Emulator, connected to the TDI / Gold Card. Image format.
5. QL-SD Microdrive replacement
6. Minerva ROM upgrade, alongside the QL-SD
7. EPROM Cartridge - e.g. Toolkit II ROM
8. Serial cable and PC file transfer
9. Network cable for linking two or more QL computers
Here's a table of some of the more notable modern peripherals and their features :
TDI GC SGC QL-SD
Card Reader: YES(CF) NO NO YES(SD)
68000/Acceleration: NO YES 020 NO
Memory: 800K 2MB 4MB NO *)
Disk interface: YES YES YES NO
Battery-backed clock: NO YES YES NO
Toolkit 2: YES YES YES NO
Minerva ROM: NO NO NO YES
*) The file allocation table requires memory
TDI = Tetroid Disk Interface
GC = Tetroid Gold Card Clone
SGC = Tetroid Super Gold Card Clone
Ql = SD=SD Card reader