I would be very disappointed if nobody ever suggested this, however since nothing was done yet, it clearly wasnt pointed strong enought.
My wish is to add to the list of Rogue special abilities some feats releated in theme with Rogue class.
The reason is variety and fun. THere is 4 slots and only 6 abilities, and its easy to find some of them do not fit the gamestyle (what is a dimplomatic way to say that they are useless).
The list to add is:
Combat Expertise - as long as our rogue is smart enought for that,
Improved Feint - since it has theoretical synergy with class. (still it could be done in other ways, but... sounds cool)
Hamstring - since "nasty debuffing attack" fits theme.
Sap - as above
Slicing blow - as above
Weapon Finease - for those who think dex based rogue is a good option. Also something for mechanics.
Precision - so rogues can do something with high fort mobs. (the state of precision is another discussion)
The presented list in any way will not make Rogues Overpowered and so on. In fact some of them are the good way to gimp the build, but... the best choice is to have a choice. And that is something we lack, and what Rogues needs.
EDIT: Good spot chek Emizand, i must though about server hamster at the moment. :-)