The weakest part of many routers on the market today is the firmware installed on it. It's often insecure, out of date, or unreliable, and it's lead to the creation of open source alternatives including Tomato and DD-WRT. While these alternatives are free, it still requires extra work after buying the router. The added complication of the installation can be a barrier for many end users. But Asus has come out with a series of routers that come with DD-WRT pre-installed.
DD-WRT is Linux-based, and has a logically structured user interface accessible from a standard web browser. Thanks to the huge user community that gives support to DD-WRT developers, security flaws and holes are found and corrected quickly. There's also extensive support and how-to guides on the DD-WRT website.
Find all of the router models with DD-WRT on Asus' website