There is No magic Routers, they disappeared when Dragons did.
The general approach that I take for Coverage issues is the following.
The best way is to lay few CAT6 cables to central locations in the house, install Access Points, or Cable/DSL Routers configured as an Access Points ( Using a Wireless Cable/DSL Router as a Switch with an Access Point ), and connect them to the Main Router.
You do not want/can not/hate/your client hate to lay Cables.
Buy a Pair of Wireless Routers that can do WDS (Zexel, SMC, Belkin have models that do WDS as is out of the Box.
Linksys WRT54GL can do WDS when flashed with DD-WRT firmware.
Using a Laptop loaded with Netstumbler, do a Wireless survey in the house,
http://www.netstumbler.com/downloads/
According to the Netstumbler's signal strength reading, identify spots that have strong signal. and spot with weak, or No signal.
Evaluate how you can cover the space and start placing WDS units.
Additional Wireless Routers in WDS Mode (Wireless Network - Configuration Modes. ) has to be placed in spots were the signal is good about Half way to the dead spots.
How many WDS units are needed? It depends on your specific environment (that is a good the reason to buying WDS units one at the time, try it, and decide on the Next step).
Otherwise.
Extending Distance -
http://www.ezlan.net/Distance.html
Wireless Router as an AP -
http://www.ezlan.net/router_AP.html
Wireless Modes -
http://www.ezlan.net/Wireless_Modes.html
Wireless Bridging -
http://www.ezlan.net/bridging.html
Hi Gain Antenna -
http://www.ezlan.net/antennae.html