My swiftblade needs a weapon

[Nosta]

I have 42000 to spend on a weapon and would like to get the best I can for a swiftblade character
as for what i'll be fighting. pretty much anything the DM can think of is a fair game. all monsters are on the table

[Snowbluff]

Wrathful Healing is pretty good. (Enemies and Allies)

Mage Bane is popular. (Magic Item Compendium)

Keen Prismatic Burst Rapier/Scimitar could be good. (SRD/Magic Item Compendium).

[Necroticplague]

More relevantly than what you fight is how you fight. Stregnth modifier? Profeciencies? Number of Arms? Possible other resources you might be willing to invest? Current primary source of damage? What are you looking to get out of the weapon?

If you're feeling cheesy, Manyfanged makes for an excellent property. Since your a Swiftblade, you might get some mileage out of a Spellstoring weapon to get an extra Haste in for the day.

[Fouredged Sword]

Obviously the swiftblade needs to wield a quickrazor.

[Darrin]

It helps to know if you favor a particular combat style, what feats you have, etc. But off the top of my head... I'm assuming you want a two-handed weapon and haven't spent any feats on something exotic/TWF/Somatic Weaponry. Two candidates spring to mind:

Elvencraft composite longbow, AKA "quarterstaff with three wand chambers". A little more expensive up front, particularly if you make all three weapons masterwork (900 GP, plus 300 GP for Elvencraft), but offers more versatility with a selection of swift action wands. Make it out of serren (+4000 GP, BoED) and it counts as a ghost touch weapon. When used as a quarterstaff it counts as a double weapon, but I'm guessing you don't have the feats available to do much with TWF, so ideally you're just gripping it as a two-handed weapon.

Greatsword. Best average damage of all the martial two-handed weapons. Avoid the temptation of the falchion or anything exotic. For materials I'm partial to starmetal (+5000 GP, Complete Arcane) for the +1d6 damage against [extraplanar] creatures, but cold iron is the material that's hardest to replicate with a spell effect or magic item.

For Weapon Properties, start with Shock (DMG) and a Lesser Crystal of Acid Assault (3000 GP, MIC). You can add Flaming via wand chamber + wand of blades of fire, and Frost via Gloves of the Uldra Savant (3100 GP, MIC). Glyph Seal (1000 GP, MIC) keyed to when drawn or when striking enemies is also a nice way to get off a 1st or 2nd level buff. After that, consider adding Psychokinetic or Screaming (MIC). If you have money left over, add some 1/day low-level spell effects for flavor or a few oddball "Nope!" situations: ray of resurgence (Lost Empires of Faerun), winged watcher (Complete Scoundrel), protective interposition (Forge of War), close wounds (Spell Compendium), and so forth.