dunno if it's been mentioned yet, but here's something that might help some people(mostly in the early game): when one sectoid is boosting another, killing the one doing the boosting will also result in the second one dying. assaults with run and gun, or good snipers are a godsend here.
i've finished a playthrough on normal (went until a terror site repeatedly sodomized my entire team, then i activated x-com heroes and stomped my way through every single encounter until i finished it ), and have now started one on easy using a mod to activate second wave features (using mainly the randomizing ones).
also, ufopedia has the entire tech tree up: http://www.ufopaedia.org/index.php?title=Research_(EU2012)
btw, what's everyone using as a squad set-up? i'm somewhat fond of one sniper, one heavy, two assaults and two supports.