Depends on which one you're using, mine contains a Radeon HD 4670. There is a lo...

Depends on which one you're using, mine contains a Radeon HD 4670. There is a lot of NVIDIA on the PCI bus but this does not seem to be an obstacle to the thing running flawlessly:

   00:00.0 Host bridge: NVIDIA Corporation MCP79 Host Bridge (rev b1)
   00:00.1 RAM memory: NVIDIA Corporation MCP79 Memory Controller (rev b1)
   00:03.0 ISA bridge: NVIDIA Corporation MCP79 LPC Bridge (rev b3)
   00:03.1 RAM memory: NVIDIA Corporation MCP79 Memory Controller (rev b1)
   00:03.2 SMBus: NVIDIA Corporation MCP79 SMBus (rev b1)
   00:03.3 RAM memory: NVIDIA Corporation MCP79 Memory Controller (rev b1)
   00:03.4 RAM memory: NVIDIA Corporation MCP79 Memory Controller (rev b1)
   00:03.5 Co-processor: NVIDIA Corporation MCP79 Co-processor (rev b1)
   00:04.0 USB controller: NVIDIA Corporation MCP79 OHCI USB 1.1 Controller (rev b1)
   00:04.1 USB controller: NVIDIA Corporation MCP79 EHCI USB 2.0 Controller (rev b1)
   00:06.0 USB controller: NVIDIA Corporation MCP79 OHCI USB 1.1 Controller (rev b1)
   00:06.1 USB controller: NVIDIA Corporation MCP79 EHCI USB 2.0 Controller (rev b1)
   00:08.0 Audio device: NVIDIA Corporation MCP79 High Definition Audio (rev b1)
   00:09.0 PCI bridge: NVIDIA Corporation MCP79 PCI Bridge (rev b1)
   00:0a.0 Ethernet controller: NVIDIA Corporation MCP79 Ethernet (rev b1)
   00:0b.0 SATA controller: NVIDIA Corporation MCP79 AHCI Controller (rev b1)
   00:0c.0 PCI bridge: NVIDIA Corporation MCP79 PCI Express Bridge (rev b1)
   00:15.0 PCI bridge: NVIDIA Corporation MCP79 PCI Express Bridge (rev b1)
   00:16.0 PCI bridge: NVIDIA Corporation MCP79 PCI Express Bridge (rev b1)
   02:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV730/M96-XT [Mobility Radeon HD 4670]
   02:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] RV710/730 HDMI Audio [Radeon HD 4000 series]
   03:00.0 Network controller: Qualcomm Atheros AR928X Wireless Network Adapter (PCI-Express) (rev 01)
   04:00.0 PCI bridge: Texas Instruments XIO2213A/B/XIO2221 PCI Express to PCI Bridge [Cheetah Express] (rev 01)
   05:00.0 FireWire (IEEE 1394): Texas Instruments XIO2213A/B/XIO2221 IEEE-1394b OHCI Controller [Cheetah Express] (rev 01)

There is some Broadcom as well - the Bluetooth controller, which works fine - as well as some Qualcomm - the wifi controller which, again, works fine.

This is a 'Late 2009 27" iMac', running the internal display as well as an external 1920*1200 24" monitor through a DP->HDMI cable. Everything works, including the silly IR remote control thingy (tested using the IR blaster on my phone).