I actually prefer the dex-based route, myself, but I'm looking for a way to optimize my dexterity modifier without using shapechange or cancer mage that are border-theoretical. Actually I have no problem with shapechange, but I don't think I'll manage to get that high.
Hrm. Well, Zeugalak can be done through Aberrant Wildshape, but you'd need Assume Supernatural Ability, and since it's a 16 HD form, you wouldn't be getting it much before Shapechange in any case.
Will O' Wisp works at lower levels, as someone else mentioned. Lots of benefits, relatively few downsides. I don't think you're likely to find a better form. Prior to 9th level, the Deadly Dancer has a pretty darned high Dex, and is only 4 HD, but is freakish-looking.