Please get ready for your arrival. Shanghai Metro, be very scared.
• Opening late 2011: Line 8 (South Gate of Forest Park - Huilongguan Dongdajie; into northern Beijing), Line 9 (Beijing West Railway Station - Guogongzhuang; bus transfer needed to Line 1), Line 15 (Houshayu - Fengbo)
• Opening September 2012: Line 9 (National Library - Beijing West Railway Station), Line 10 (Jinsong - Bagou via Songjiazhuang, Fengtai and Gongzhufen; yep, it's the other side of the loop)
• Opening December 2012: Line 6 (Haidian Wuluju - Caofang), Line 8 (Huilongguan Dongdajie - Zhuxinzhuang; northernmost link; also Beitucheng - China Art Museum)
• Likely opening up late 2012 (latest early 2013): Line 14 (Zhangguozhuang - Lize Business District; will connect with Lines 9 and 10)
• Opening 2013 - 2015 with certainty: Line 6 (Caofang - Dongxiaoying; into eastern Tongzhou), Line 7, Line 14 (Lize Business District - Shan'gezhuang; that's the Wangjing - CBD - Beijing South express), Line 15 (Wangjing West - Beishatan), Line 16 North, Changping Line (Nanshao - Ming Tombs Reservoir Park), Mentougou Maglev, Western Suburban Line, Yanfang Line (extends Fangshan line further west)
• Likely also to open between 2013 - 2015: Line 3 East and West (yep, not the central bit; weird, isn't it?), Line 6 (Haidian Wuluju - Pingguoyuan), Line 8 (China Art Museum - southern Beijing), Line 15 (East Gate of Tsinghua University - Beishatan); Line 16 (entire line), Changping Line (Xi'erqi - Jishuitan), Line 17 (northeastern link to Tiantongyuan)
• In the pipeline... may open by 2015: Line 9 North, Line 12 (part), Fangshan Line (Guogongzhuang - Mengjiacun), Airport Link (from Terminal 3 through CBD and Beijing South to 2nd Airport), as well as an extra line in the CBD and the S6 Suburban Railway
• 2015 - 2020: Line 3 Central, Line 11, Line 12 (remaining part), Line 18 (for much of the 4th Ring Road); probably Express Subway Line 1.
By the way, from what your Beijingologist has seen, Line 3 will bring a stop bang in the middle of Sanlitun. Don't dare budge an inch, Apple Store Sanlitun and Bookworm; y'all are sitting on gold (if the plans work out)...