a farseer is a must for a
HQ but i would avoid the farseer powers and go for divination and telepathic.
the spirit seer is also very good at buffing the ability of units and i would keep him using the warlock powers.
you cannot go wrong with wave serpents that is for sure, put some wraith guard in there with D-scythes and watch your opponents miniatures melt away.
guardians are very useful all round but will melt under fire unless buffed with powers or sitting in good cover.
casting invisibility on a wraithknight is also a good way to keep him alive from all the firepower coming his way.
dire avengers are very useful as they can give phoenix lords an invulnerable save but more important they can do the dance of blades in the form of moving into range of there weapons and then using battle focus and fleet to move back out of range of mass return fire. also good at shredding big nids.
warwalkers are also very good at popping in and out of cover with battle focus and give them one upgrade and they get 3" to there fleet roll. i like to give them bright lance and scatter laser in the classic fashion as it make them very versatile vs just about everything.
jetbikes are very useful and cheap (points wise) allowing you to zoom across the board to take objectives and shred units.
there are some horrendous power combinations you can do such as suing the warlock power horrify along side some of the telepathic powers to really mess with peoples minds but will require getting the correct powers.
hope this gives you something to think about