The best value in 802.11b adapters are the Agere Orinoco clients. To use one in Linux, you'll have to buy the Orinoco PCMCIA client + a PCI adapter.
To give you an idea of what the difference might be like, in my setup, an Orinoco client outperformed a D-Link DWL-650 (based on the very popular Prism2 chipset that most popular manufacturers used) by roughly a factor of 3.