1-18: common vendor 2hs
19:http://db.vanillagaming.org/?item=4818
dope vendor sword on a freshly launched server, get it from the goblin while questing in stonetalon horde side.
at 26: http://db.vanillagaming.org/?item=12249
30+ WW Axe or if you're pro you can go for the first Lo'Grosh kill and there's a 30% chance http://db.vanillagaming.org/?item=6327 will drop
Mid 40's Thrash Blade is usually the only efficient option since decent 2h are harder to come by. That being said, Executioner's Cleaver if you manage to buy one or you can try your luck in Uldaman. If you're a sperg who wants a big 2h to fulfill your roleplay fantasy, then you can eventual settle for the axe off Rotgrip.
50+ not many options pre 1.10/1.4 apart from a 2h off emp and a couple of BoEs, so you can't rely on getting any upgrades before you hit 60.