WlanSettingsBackup is a project mainly written in Java, it's free.
With Wlan Backup & Recovery you can backup your wlan config file to SD-Card with the opportunity (needs root privilege!!). Tested on Android 2.2 / 2.3
Wlan Backup & Restore saves the backup file on the root folder of your SD-Card. The backup file name is "wpa_supplicant.conf.bak" (!!!caution: your WLAN Keys are stored in clear text!!!).