I dunno why everybody plays flat burst damage rengar still (I mean, I got my first rengar penta with that build, but that was before the nerfs.)
100% Crit rengar is the way to go
Triforce + IE + PD + Atma's + Ninja Tabi + BT + Crit runes
Jump out of a bush / stealth, let the attack land (as in, don't use your Q until you hit the person, for a total of 3 hits instead of 2. Alot of people don't realize that rengar's Q procs on his jump)
Double Q = Complete and utter rape, then that double attack speed bonus boosts you up to around 2.0 attack speed, continue to destroy star fish with him.