I heard that starting off with either Doran's Shield (if laning vs physical) or Null Magic Mantle +2 Pots (if vs magic) works best. Either way, you end up going for a Spirit Visage which lets you use bloodlust more often for more effect.
this may be more effective come his remake with the new way his bloodlusts will rack up.
also for those saying arpen runes and getting starks etc. i disagree, for tryndamere. the reason is you do not want to stack flat arpen on tryndamere IMO. everybody will eventually be getting some massive armor item against you, or a couple, and everybody already has 80-100 armor from the get go anyway.
stacking flat arpen (including runes masteries etc) the max arpen you can have is 116. 146 if you use sword of the divine. AND in order to get this you need to have arpen marks/quints + 3 item slots (starks, youmuus, black cleaver). now you only have 1 more item open for you, since you will have boots and IE. this is not exactly ideal for tryndamere IMO.
you want last whisper. keep those crit chance runes, or defensive runes w/e you want to run, that frees those up. build up your damage and a little attack speed + last whisper.
im not sure about SR, i don't really play tryndamere much on SR anymore but when i play on TT (trynd is god on TT) i personally like to rush executioners calling. great early/mid game item of crit/lifesteal and will let you hit the jungle without losing a lick of your life. then i'll grab a recurve bow/boots and start working on IE.
the reason why i put my damage on hold at first is because you have such a massive damage bonus in bloodlust, you can afford to place it on hold a little bit longer than anybody else.
now you start working on your IE starting with bf sword obviously. afterwards you go straight into last whisper, you'll need it by then. now you can keep working on your damage with bloodthirster. from here you sell your exe calling and get another bf sword working it to another bloodthirster eventually.
you can also upgrade your recurve bow to a wits end or SOTD whenever you want.
wits end is an awesome item either way. gives you mr and basically +42 damage on every strike, but it doesn't give you more attack speed, so SOTD is decent too, but you probably won't use the active.
on SR instead of getting exe calling i'd probably get a wriggles, since it is that amazing. either way you need that lifesteal.
few points about my build. final build looking like boots (zerker or swiftness), IE, LW, BT, BT, SOTD i'll say....why no phantom dancer?? First off it does not give you any damage. tryndamere is about hitting hard, not hitting fast. you already have a good attack speed item in SOTD or wits end, and you do not need more attack speed than that. you do not need 100% base critical in the least. 50% base crit chance is more than enough and its some what of a wasted stat IMO getting anything over it. you can get 50% with just runes, your +10% at lvl 1 and IE. your passive will take care of the rest.
also you do not need to crit every single time because you will be hitting like a truck regardless.
last whisper is a must. you will be hitting so hard (and still plenty fast) people will be stacking massive armor to 'counter' you. last whisper is an absolute must.
damage and lifesteal. you have all the crit you need in IE/runes/masteries/passive etc. you have all the attack speed you need in boots/masteries/recurve bow. you want damage and lots of it, and lifesteal will always help tryndamere especially when you spin to that jungle camp with ignite on you just before your ult runs out. yes you can easily lifesteal through it and live.
couple points about tryndamere. your early game is only bad if you're up against a duo lane. try to get a solo you'll manage much better (or jungle).
once you stack your bloodlust stacks and have +40 damage, be aggressive and hit them a couple of times (hopefully crit too). you'll do more damage than they can any day! If they get low enough feel free to take the kill and be fed.
a death for a kill is necessary on tryndamere. be aggressive and get that kill even if it means you die. the gold is put to much more dangerous use on you than it is on them.
you do not need to stack attack speed. most of the time the enemy team will not let you stand there auto attacking 2.5x per second anyway, so make the hits you get in count with high damage and arpen instead of low damaging crits because you want to stack PDs and run fast.