My list changes depending on who I am playing, but I mainly use the two Exarchs against Tau, backed up by an waveserpent rush loaded with scorpions. Assulty armies work best against Tau, I have found. This is as much of my list that I can remember...
HQ: 1 Farseer, singing spear, runes of witnessing, guide
HQ: Kurandras
Troops: 2 defender squads, 10 men in each (including gunners), scatter laser for each squad
Elites: 2 Striking Scorpion squads, 9 men in each, one squad has an exarch with Scorpion's claw, the other is led by Kurandras
2 Waveserpents, spirit stones (each), 1 brightlance, 1 starcannon
Heavy: Falcon, CTM, Starcannon
Fast: 2 Swooping Hawk squads, 4 men and Exarch (each) w/ Web of Skulls and Surprise assult
That comes out to somewhere between 1500 and 1750, if I played a bigger game, any extra points would go into some more heavy support, or some vypers. This list is changing, though, with the new vehicle rules, which make my rush suicide. This is why I am inquiring about the Hawks... They are the assult squads I am keeping, here. The scorpions will have to go.