With its help, (and some encouragement from Progress Quest,) I designed the following:
Incremental, Elemental Keen Rapier of Antipode
175,000gp to purchase (Guesstimate)
1d6+(Lv/5, round down) Damage
1+(Lv/10, round down) To-Hit Bonus
Threat Range 15-20 (Rules Lawyers: DMG Errata says that a few DMG's were printed saying Keen = Slashing only. Correct statement is Keen = Slash & Piercing only)
On command, Rapier is sheathed in Fire, Ice, or Lightning, (One at a time) and deals an additional 1d6 of appropriate elemental damage.
If Wielder is 15th Level or Higher, can use two elements 1x/Day for a total additional elemental damage of:
Fire & Ice: 2d6+2
Fire & Lightning: 2d6-1
Ice & Lightning: 2d6+1
If Wielder is 30th Level or Higher, can use all three elements for 3d6+1 damage, and 1d6 backlash damage per ATTEMPT.
Dispels as a level 25 spell. After a successful dispel, Rapier acts as a Keen Rapier. 3 days later, abilities regenerate at the rate of 1/day (DM discretion or Random Roll)
If dispel is successful by a margin of 10 levels or greater, Rapier deals 1d6 multi-element damage to wielder and 1d4 damage to all within 10 feet, and is destroyed.
Unable to be purchased / Unique Item
1d8+5 Damage + 1d6 "Holy Burst" (See Text)
+5 To-Hit Bonus
Counts as Bastard Sword (I'll have to look up the mods for this later)
Threat Range 15-20 x3
Holy Burst: Weapon deals 1d6 of Holy damage to target, 2d10 Holy damage on critical or vs. Undead.
As a full-round action, may be used to heal 2d8+3 damage to any ally within sight.