What are the best enhancements for a rapier?

I am playing a character whose base class is a swashbuckler. But I did not optimize it to be a great warrior because for once I decided to rather invest in relationships and feats related to eberron, and I enjoy playing this way. But as a consequence, my fighting power did not improve at all while passing levels; my base attack bonus did, but I am still dealing (1D6+strength bonus+int bonus) damage as when I was a low level.

We recently seized some gold pieces and have the possibility of buying magical enhancements for our weapons, so I am looking for the best way of improving my damage rate. Do you know of special rapiers, or of effects that are especially effective on a rapier?

EDIT: I think I should give additional details on what books are allowed. The universe is Eberron, so imports from others universes like Forgotten Realms, Faerun, Oriental Adventures, are not allowed. In Eberron the DM proposed the use of the Action Points and DragonMarks system which already adds improvements to the gameplay on its own, and as a consequence, other alternative gameplays like psionnics and related (for example the collision effect) are not allowed. Finally, some books a little too much unbalanced like the Tome of Battle and Sword and Fist and all dragon fight related books are disallowed… which still lets a lot of books allowed, I think to all complete xxxx supplementals, most compendiums, plus the base rulebooks and anything else matching the general spirit of being evenly balanced and not being part of a specific universe or additional ruleset system beside Eberron.

Since this question could possibly be used as a reference for another swashbuckler not having the same constraints, don’t hesitate proposing though, even if I can’t use it, it’s still interesting knowing it exists.

Some additionnal details on myself now. I am currently swashbuckler 5/dragonmark heir 2/duellist 1. For further progression I am aiming swashbuckler 5/dragonmark heir 4/duellist 3/blade of Orien N. I have the dragonmark of passage and I use it a lot to teleport in combat. I also invested a lot of skillpoints in movement skilltricks and in movement or relational skills like tumble, jump, balance, diplomacy, sense motive, bluff.. Without wearing magic items, my current abilities are DEX-18, STR-12, INT-14, CON-14, WIS-10, CHA-10

There is already a lot of replies, thanks a lot everybody, I apologize for not having given more details earlier. I will let the question open for a while since I also need time to explore all of your suggestions.