Are you an AmigaOS 4.1 Classic user? What hardware is working for you? Post a comment if you have something working and I will update the list!

Here is a work-in-progress list:

AmigaOS 4.1 Classic Compatibility Hardware list
[updated June 15, 2015]

Amiga Computers (requires one of the PPC processor cards listed below)

Amiga 1200, 3000(T) and 4000(T)

Note: on-board SCSI of A3000 and A4000T is not supported, use the SCSI controller on the Cyberstorm PPC processor card which is fully supported with a native DMA enabled driver, or the on-board IDE controller in the Amiga 1200 or 4000(T), or one of the IDE controllers listed below.

Processor Cards

phase5 or DCE Blizzard PPC (all models – no SCSI driver yet)
phase5 or DCE Cyberstorm PPC (all models)

Memory Expansions

ZorRAM 128MB or 256MB (Amiga 3000(T) or Amiga 4000(T) only)
DKB 3128 Zorro Memory Card (Amiga 3000(T) or Amiga 4000(T) only)
Indivision’s BigRamPlus 256MB RAM (Amiga 3000(T) or Amiga 4000(T) only)
Generic Zorro 3 memory support (in theory any Zorro 3 memory should be found and configured automatically)

PCI BusBoard Expansions

Elbox Mediator A1200 (all models)
Elbox Mediator 3/4000 (all models including the new MK-II version)
Maytay Prometheus
Firestorm (upgraded Prometheus)
DCE GREX 1200 or 4000 – Support for Voodoo 3 and RTL8029 ONLY! Experimental Support in Amiga OS 4.1 Final Edition and up.

Zorro Backplanes

RBM Towerhawk Zorro backplane
Elbox ZorroIV (Winner Z4)

A quick note about PCI cards in general: There are many different types of cards, with different BIOS, firmware, voltages, and circuit board layouts.  Therefore each card must be tested in your own machine to see if it works.  Even if a card is listed here it does not guarantee it will work in your machine due to the reasons above – you just have to try it.

Graphics Cards (PCI)

Sapphire ATI Radeon 9250 PCI 256MB (128MB visible) (card is 3.3 Volt or 5 Volt)
Elbox ATI Radeon 9250 PCI 256MB (5 Volt only)
Elbox ATI Radeon 9200 PCI 64MB (5 Volt only)
Radeon 9200 256MB (RV280/M9+) (3.3 Volt card working in modified 3.3 volt A4000 Mediator)
3DFX Voodoo Banshee 16MB PCI (no Warp3D, no overlay, no hardware pointer)
3DFX Voodoo 3 16MB (including Warp3D and DDC)
3DFX Voodoo 4 32MB (including Warp3D)
3DFX Voodoo 5 64MB (only 32MB recognized, including Warp3D)

Graphic Cards (Zorro)

Picasso II or II+
GVP Spectrum
Graffity
Picasso IV
Piccolo
Piccolo SD64
Retina Z3 (Altais)
Pixel64
Merlin
Domino
Cybervision 64
Cybervision 64/3D

Graphic Cards (other)

Cybervision PPC 8MB Permedia 2 (including Warp3D – beta)
Blizzardvision PPC 8MB Permedia 2 (including Warp3D – beta)

USB

Deneb USB Controller (requires Poseidon 4.x)
Subway USB Controller (requires Poseidon 4.x)
Highway USB Controller (requires Poseidon 4.x)
Algor USB Controller (requires Poseidon 4.x)

Network Cards (PCI)

Realtek 8029(AS) based PCI network card

Network Cards (Zorro)

Commodore 2065 (requires user supplied driver to be placed in DEVS:networks)
Zeus ConneXion (C= 2065 clone) (requires user supplied driver to be placed in DEVS:networks)
VillageTronic Ariadne II (requires user supplied driver to be placed in DEVS:networks)
X-Surf (needs driver version 1.4 or higher).  The on-board IDE does not work.
X-Surf 100

SATA Controllers (PCI)

Sabrent 2 port SATA Raid PCI controller (Silicon Image 3512 chipset) (5V compatible)
No-Name 4 port SATA PCI Controller (Silicon Image 3114 chipset (5V compatible)

IDE Controllers

Silicon Image 0680 based PCI cards (Firestorm only)
Elbox FastATA 1200 MK-III (PIO-0 to PIO-5 modes supported)
4 port adapters IDEFix, EIDE99, FastATA (using scsi.device)

SCSI Adapters/Converters

ACard AEC-7720UW SCSI to IDE converter (Tested in A4000)

Sound Cards (PCI)

Generic PCI Sound Card, Model SCBAS104, ESS Solo-1 1969 chipset (5V Compatible)
Terratec ESS Solo-1 (TTSOLO1-N VER1.1)
ESS Solo-1 (1938 chipset) – confirmed by one user Note: not all variants of this card will work
Soundblaster 128 (see post here on instructions)

Sound Cards (built-in or Zorro)

Paula
Concierto IV (Picasso IV add-on sound card)

TV Tuners and video encoders

VillageTronic Picasso IV – Paloma IV (needs modification of kicklayout as documented in FAQ)
VillageTronic Picasso IV – Pablo II

Other Peripherals

Thermaltake BlacX ST0005U e-SATA Hard Drive Dock
(e-SATA bracket or backplate and working SATA PCI controller card required)

Known incompatible Cards:

phase5 FastLane Z3 (machine will not boot with card installed)
DCE GRex 1200 and 4000 (no complete documentation available) – Experimental Support in AmigaOS 4.1 Final Edition and up (See PCI BusBoard Expansions above)
AlienDesign Repulse Sound Card

Notes:

USB devices compatible with Poseidon are not listed here.  They all should work except for USB Sound cards which require an additional file named usbaudio.a.main to be placed in LIBS:  After a cold restart your USB sound card should be available in AHI prefs.  Poseidon must be started in order for the sound to work.