Routers

Netgear WNDR3300. Uses Broadcom wireless (binary module), somewhat supported by OpenWrt.

Netgear WNDR3700. Uses Atheros wireless (FOSS). Ships with a modified OpenWrt 7.09. Support in OpenWrt trunk is ongoing.

D-Link DIR-825 B1. Uses Atheros 9220/9223 radios, and Atheros 7161 CPU. Supported by OpenWrt trunk (blog post with details).

DIY kits

Boards

Ubiquity Networks RouterStation Pro. Netgate sells a nice board, enclosure, and power supply kit.

Radios

Ubiquity Networks SR71-A. mini-PCI dual-band 802.11abgn card. Uses Atheros AR9160 radio.

SparkLAN has a good selection of mini-PCI and mini-PCIe radios, with Atheros and Realtek radios. Recommended from OpenWrt forum.