Linksys ships high-gain replacement router antennas
Linksys says the dual-band antennas will deliver gain of 4dBi in the 2.4GHz frequency band and 7dBi in the 5GHz band, compared to the 2.5dBi and 3.5dBi gain respectively that the average stock antenna provides. The omnidirectional antennas use standard RP-SMA connectors, so you should be able to mount them to just about any router with upgradeable antennas.
The antennas, sold in two- and four-packs for $60 and $100 (models WRT002ANT and WRT004ANT respectively), are available now. I've asked for eval samples and expect to have a hands-on review in the next couple of weeks.
Why this matters: Upgradeable antennas mean you may not have to buy a whole new box to get better Wi-Fi. The antennas should deliver a significant bump in horizontal range, but if you're having difficulty reaching a wireless client (a smart TV, a streaming box, a laptop, or what have you) on a floor above or below the router, you'd be better off with a power-line range extender or stringing ethernet to a wired access point.