I run the ATI X700 Pro (AGP 256 MB) card, which retails for $200 and is well beyond the needs of WB5.
Therefore, if you decide to upgrade your card, you could easily go with an ATI (9600, 9800, X700) series, or for nVidia (5500, 6600) series.
The series numbers indicate the chipset model produced by these companies, all of which you can find on third-party vendor's circuit board adapters for various prices (ASUS, Gigabyte, MSI, eVGA, Powercolor, etc.)
ATI also offers their own brand card which includes their chipset and circuit board adapter.
You should be able to find an adequate card between $70 and $200, depending on which chipset you choose.
Note - this assumes you have an AGP slot, and are not considering using a legacy PCI slot video card - which may provide a little improvement based on increased memory (say a 128 MB card), and perhaps better efficiency in displaying images - but nothing like an AGP card.