A newer alternative for WLAN performance improvement - at least for those who don't have "enterprise-grade" budgets - is wireless repeating. This method has actually been around almost since access points themselves, but was available only in commercial-grade APs - with commercial-grade (>$300) pricing!
That all changed in the Fall of 2002 when D-Link introduced a free firmware upgrade to their DWL-900AP+ access point that brought the cost of 802.11b wireless repeating down to about $100! [See Wireless Repeating with the D-Link DWL-900AP+ NTK for more info.] D-Link has pursued this product category the most aggressively, introducing the lower-cost (about $70) DWL-800AP+ that omits some of the 900AP+' s access point modes.
A wireless repeater is basically an AP with a special mode that re-transmits data received from other wireless stations over the same wireless channel. This means that all you need is a repeater and a power outlet to extend the range of a wireless LAN! Figure 4 illustrates the use of a repeater.
Figure 4: WLAN with wireless repeater
This magic comes at a price, however. When running in repeater mode, the AP's Ethernet port no longer passes LAN traffic, and becomes instead the only way to access the admin interface of the repeater. So you really don't want to locate repeaters in hard-to-reach places, because rebooting them when they inevitably lock up will be a major pain.
You also lose about half the normal throughput for each repeater, making a 5Mbps link into one running at about 2.5Mbps. This probably isn't as big a deal as it might sound if you mainly use your wireless LAN for email and web browsing with one or two clients. But if you have a very fast Internet connection or do a lot of file transfer / downloading, you probably won't be satisfied with a wireless repeater's performance.
Although some products allow repeaters to associate with each other - forwarding wireless data through multiple repeaters for longer range extension - others limit the repeat to one "hop" or repeater unit. Even in the latter case, however, you can have multiple repeaters associated with a single AP, which at least will let you extend your WLAN's range in a ring around the AP.