Open the system Control Panel, by typing Win+Break or going to My Computer and clicking on System Properties.
Click on your Windows Experience Rating to go to Performance Information and Tools
Click View and Print detailed system information
Scroll down to the Graphics section. If you have the proper drivers installed for your card, it should say under "display adapter type" what kind of graphics card you have.
All the specified methods are fine as long as you have graphic card drivers installed. Here's what to do if you don't: In Device Manager, right click the Unknown Device (that you assume is the graphics card), select properties and go to Details tab. Select Hardware IDs from the Property drop list. Right-click and copy any of the values and paste it on http://devid.info/en/
Use a tool like GPU-z
Wow, great answers -- and I have a fourth way!
Click the start menu (or press the Windows key) and type "Device Manager", then launch Device Manager. If you're a command line kind of person execute
From here expand Display adapters to see what kind of video card you have.
You can right click the display adapter and select properties to see even more detail.
The existing answers are all for Windows.
In Linux you can use lshw to get information on pretty much any piece of hardware in the PC.
lshw -short lists everything, look for
$ sudo lshw -short H/W path Device Class Description ====================================================== /0 bus Rampage II GENE /0/0 memory 64KiB BIOS ... /0/100/3/0 display G98 [GeForce 8400 GS] ...
lshw -c display gives more detail on the graphics:
$ sudo lshw -c display *-display description: VGA compatible controller product: G98 [GeForce 8400 GS] vendor: nVidia Corporation ...
So in this case, the graphics card is an nVidia GeForce 8400 GS.
If you want to know and there aren't any drivers installed here is a nifty way of doing it:
Open up a command prompt (winkey + r, write cmd, hit enter) In this prompt type: debug (hit enter) In the debug program write: d C000:0010 (hit enter)
EDIT: I realize that you may not have debug.exe if you run windows 7. If you get "IB M VGA Compatible BIOS." you can continue through the memory with "d" (enter, no quotes) where it may show a string like "Nvidia XXXXX" or ATI "XXXXX".
If you, however, are using an onboard graphics card you may not get another string than "IB M VGA Compatible BIOS."
Anyways its an old school way of getting the graphics card that may not be applicable for your motherboard and/or OS (windows 7 enterprise as example, pro version is ok though.)
It may however save you some trouble from time to time when you are fixing your "friends" computers still running other versions(XP) or specific versions of 7 (Can't say if it works for Vista, never ran it)
Take this at facevalue. Personally im saving this for when i need it, a 2 - 5 years old computer, that you promised to fix and re-installed but you can-not-find-the-drivers for kind of scenario.