Now that the Advance Class Guide is out, the answer has changed (as @Lord_Gareth suggested it would in his January 2014 answer).
As of today, there are two published feats that expand the set of finesse weapons:
1. Dervish Dance
(which requires a 13 DEX, Weapon Finesse, 2 ranks in Dance, and proficiency in the scimitar) lets you count a scimitar as a finesse weapon (and add DEX instead of STR to damage)...as long as it's sized for you, used one-handed, and your other hand doesn't hold a shield or weapon.
2. Slashing Grace
(which requires a 13 DEX, Weapon Finesse, and Weapon Focus) lets you use DEX (instead of STR) for damage with any one handed or light slashing weapon one has Weapon Focus in. As with Dervish Dance the weapon has to be sized for you, but it doesn't prohibit holding a weapon or shield in one's off hand.
Note though that it doesn't allow one to use DEX to hit with a one-handed slashing weapon unless one has at least 1 level in swashbuckler. Swashbuckler's get the Swashbuckler's Finesse ability which says:
a swashbuckler gains the benefits of the Weapon Finesse feat with light or one-handed piercing melee weapons.
That combined with this text from Slashing Grace:
When wielding your chosen weapon one-handed, you can treat it as a one-handed piercing melee weapon for all feats and class abilities that require such a weapon
lets swashbucklers (but not others with Weapon Finesse) use DEX to hit with a longsword or similar weapon. (A fighter with Weapon Finesse and Slashing Grace can gets DEX to hit with her rapier but still used STR for damage. If she switches to a longsword she gets DEX to damage but is back to using STR to hit.)
Also note (as per the original question) that Slashing Grace makes a bastard sword a finesse weapon for swashbucklers...but only while wielded one-handed.
Why No Love For Rapiers?
As an aside, Jason Bulmahn (Lead Designer) has said that DEX to damage was a late addition to Slashing Grace, and the design team didn't realize that it made a longsword significantly better for a swashbuckler than the more iconic rapier. To solve that, they've announced that the following feat will be released in the upcoming Pathfinder Player Companion: Advanced Class Guide Origins:
FENCING GRACE (COMBAT)
Your extreme style and fluid rapier forms allow you to use agility rather than brute force to fell your foes.
Prerequisites: Dex 13, Weapon Finesse, Weapon Focus (rapier).
Benefit: When wielding a rapier one-handed, you can add your Dexterity modifier instead of your Strength modifier to that weapon’s damage. The rapier must be one appropriate for your size.
In addition, if you have the panache class feature, you gain a +2 bonus to CMD against attempts to disarm you of your rapier while you have at least 1 panache point.