Revised list- in the running:
1) Focused Talent: Shaper (PSP p141): Minor Creation & Shaped Consciousness as Daily powers. Appeals to me very much from a RP perspective, but isn't the strongest from a mechanics view. Strongest mechanical aspect- Shaped Consciousness lets me extend the range and change the angle of attack with his Psion powers, 1/day
2) Sacrifice to Caiphon (DMA p50): if you miss all targets of a Warlock Encounter power, take damage equal to the power's level to recover the power. Tasty & powerful, but as a multiclassed PC, he won't have as many Warlock encounter powers as would be typical for his class- admittedly, only one less.
3) Rod Expertise
+1 Feat Bonus to implement att rolls you make with Rods (+2 at 11th, +3 at 21st), as well as +1 Shield bonus to AC & Ref. Boosts attacks and 2 of my defenses, including the AC I've been whining about.
Saving for later:
1) Bludgeon Expertise
+1 Feat Bonus to hammer/mace att rolls (+2 at 11th, +3 at 21st), as well as +1 Feat Bonus to push/slides with hammers/maces. Synergizes with Eldritch Strike well- hold on to this for if/when I retrain Eldritch Blast to Eldritch Strike. (8th & 10th level slots already allocated.)
Out of the running for the foreseeable future:
1) Melee Training PHB2 p187/HotFL p316: Choose ability other than Str- make MBAs w/proficient weapon using that stat's bonus for Att rolls & 1/2 bonus for damage. As per multiple advisors- not needed if I retrain Eldritch Blast to Eldritch Strike.
2) Durable PHB1 p194: +2 Healing Surges. Tough enough for now, and I get Dwarven Durability at Paragon- reconsider if/when Sacrifice to Caiphon proves too dangerous.
3) Toughness PHB p201: gain +5HP per tier. See my notes on Durable.