There may be rulings that make this one not work, and it may be old news, but...
A strong titan bloodline grants Use Oversized Weapon, as the titan ability at level 12. That ability reads as follows:
Oversized Weapon (Ex)
A titan wields a great, two-handed warhammer (big enough for Gargantuan creatures) without penalty.
For a titan, which is already a huge creature, this is no big deal. However, a
halfling with a strong titan bloodline, you have a small creature wielding a gargantuan warhammer. If you put down that warhammer and use a psionic tattoo of Compression, you can shrink down to diminutive, but you still have Use Oversized Weapon, meaning you can pick that gargantuan warhammer right back up.
Next, you cast Giant Size at a caster level of 19 or better, which increases your size all the way to colossal. An increase of seven size categories. Your warhammer
also increases in size by seven size categories, making it six size categories beyond colossal, and off of any weapon damage chart I know of. However, extrapolating off of the A&EG charts, it would be 40d6 base damage or better.