Greatwyrm
Been here a while...
In general, most of the same stuff you can use for weapon feats can be taken for Eldritch Blast. Weapon Focus, Specialization, Improved Crit - all of that stuff should work.
I know you were asking for feats, but consider multi-classing as well. I had an interesting build for an NPC that was a warlock/rogue. He used a longspear, eldritch blast, hideous blow (the one that adds EB damage to a melee attack), and (ideally) sneak attack all in combination. I'm sure hardcore char-op guys could do a better job, but he was fairly powerful for an 8th level character. I think a warlock/scout build would be pretty good too.
I know you were asking for feats, but consider multi-classing as well. I had an interesting build for an NPC that was a warlock/rogue. He used a longspear, eldritch blast, hideous blow (the one that adds EB damage to a melee attack), and (ideally) sneak attack all in combination. I'm sure hardcore char-op guys could do a better job, but he was fairly powerful for an 8th level character. I think a warlock/scout build would be pretty good too.