1.Root it
2.Use Root Explorer to navigate to /data/misc/wifi/
3.Copy wpa_supplicant.conf to SDCARD
4.Use Txtpad to read wpa_supplicant.conf

Example:

ssid="Thomson87694C"
key_mgmt=NONE
group=WEP104 WEP40
auth_alg=OPEN SHARED
wep_key0=d14a8a71fd
priority=47
}

Best way to backup is uploading wpa_supplicant.conf to Dropbox using Droidbox free , so after u wipe all data on phone/card u can simply download that file and put it where belongs

UniversalRoot + Root Explorer (txtpad -> market)