Both of these series have a third novel each due to be released this year.
Gears of War: Anvil Gate is due out August 31st.
Mass Effect: Retribution is due out July 27th.
I have read both of the first two novels from each series and they were very good (not in terms of being literary masterpieces, but in terms of expanding on the universe behind the games). The next Mass Effect novel is apparently something of a sequel to Mass Effect 2 *spoilers* examining the illusive man deploying experiments based on Reaper Technology.
I have no idea what the next Gears of War novel will be about, but I assume it has to pre-date the final game in the trilogy.
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