Yapper_Wireless via eBay offers the refurbished Unlocked Apple iPhone 4S 16GB Smartphone for GSM Networks in Black, model no. MD234LL/A, or White, model no. MD237LL/A, for $199.99 with free shipping. (Groupon offers it for the same price.) That ties last week's mention as the best price we've seen. (It's also a current low for a refurb by $31.) It's compatible with GSM networks such as AT&T, T-Mobile, and Vodafone; it can't be used with CDMA networks such as Verizon or Sprint.
A 60-day warranty applies, but it's unclear who backs it.