Feats that make cc skills, class skills.

[Evilhalfling]

The feat is also called cosmopolitan in Wheel of Time,
+2 to one skill, that skill becomes a class skill.
I have had NPC's use it, but never a PC.
It seems perfectly reasonable, possibly underpowered. Many people on Enworld have abandondend the crossclass system entirely. I have regional skills, so if a new character really needs something for the build, they normally
can find a region where it is avalaible.

 

[uzagi_akimbo]

"Versatility" is a pretty nice short-cut ( indivdual skill-choices are to be GM-approved, though ) when you actually cannot afford to loose yet another caster level in multi-classing by taking one more class to qualify for a PrC requirement due to some strange skill you are supposed to have. Often the far more sensible choice for multi-classed non-humans, who far more easily encounter an xp penalty.

 

[Darklone]

Pimping Kalamar alarm:

Skill Prodigy allows you to take you (Int bonus) # skills as class skills.

 

[CRGreathouse]

Versatile is one of the more popular feat choices in my games.