I'm using OpenWrt with following customizations to send temperature readings to EmonCMS. Hardware is noname Ralink RT3052 router (WR512-3GN) and Dallas DS9097U compatible USB 1-wire adapter. Main reason for going with Image Generator instead of compiling custom firmware was to keep binary and API compatibility with packages from stock OpenWrt repository. Package selection below leaves 168kB free on JFFS2 filesystem. Drop editor, Luci etc. and you'll have a lot more free. If you don't need to patch init scripts like I did due bug in WR512-3GN support you can simply install packages and apply scripts over top of official OpenWrt release flashed to your router.