Once you reach 20,
Staff of Battle will take you to 37 when Yak weapons start to proc. I had minimal trouble maintaining aggro with this weapon during my 20's and 30's (I did have haste, though).
There aren't many options to choose from as far as proccing weapons go pre-37 since the ratios are just terrible, and you will depend solely on weapon procs for aggro.
During Velious, a few options open up, such as
Poisoned Whip (procs at level 1),
Venom Axe (Procs at level 1),
WESS (Procs at level 1),
Wavecrasher (procs at level 1) among others. Theres are just the tradeable options.