Linux will work with all video cards in text mode, VGA cards not listed below probably will still work with mono VGA and/or standard VGA drivers.
If you're looking into buying a cheap video card to run X, keep in mind that accelerated cards (ATI Mach, ET4000/W32p, S3) are MUCH faster than unaccelerated or partially accelerated (Cirrus, WD) cards. S3 Trio64 based cards with 2 megs DRAM go for around US$160 and S3 868 based cards with 2 megs DRAM are around US$200.
``32 bpp'' is actually 24 bit color aligned on 32 bit boundaries. It does NOT mean the cards are capable of 32 bit color, they still display 24 bit color (16,777,216 colors). 24 bit packed pixels modes are not supported in XFree86, so cards that can do 24 bit modes to get higher resolutions in other OS's are not able to do this in X using XFree86. These cards include Mach32, Cirrus 542x, S3 801/805/868/968, ET4000, and others.
Most currently available Diamond cards ARE supported by the current release of XFree86. Early Diamond cards may not be officially supported by XFree86, but there are ways of getting them to work. Diamond is now actively supporting the XFree86 Project.
No, I do not know when support for these cards will be finished, please don't ask me. If you want support for these cards now get Accelerated-X.
Commercial X servers provide support for cards not supported by XFree86, and might give better performances for cards that are supported by XFree86. In general they support many more cards than XFree86, so I'll onlys list cards that aren't supported by XFree86 here. Contact the vendors directly or check the Commercial HOWTO for more info.
$199, X Inside, Inc. <info@xinside.com>
Accel-X supports most cards in 16 and 32 bpp modes and it also supports 24 bit packed pixel modes for cards that have these modes, including ATI Mach32, Mach64 (1280x1024@24bpp), ET4000/W32p, S3-866/868/968, and more. Accel-X also supports other input hardware like graphics tablets and touchscreens.
Accel-X also supports XVideo (Xv) extensions (on Matrox Comet, Marvel-II, and SPEA ShowTime Plus), PEX, and XIE.
$199, Metro Link <sales@metrolink.com>
Metro-X supports more boards than XFree but less than Accel-X, however I don't have much more information as I can't seem to view the PostScript files they sent me. Mail them directly for more info.