I think my two top choices are Skill Mastery then Slippery Mind. Unless the Rogue has a Will save that is better than his Reflex save, then Slippery Mind is a better choice than Improved Evasion.
Skill Mastery is a mixed bag. With opposed rolls, if your opponent has a better score than you, you're increasing your chances of failure by using Skill Mastery. If you have a better score than your opponent, you increase your chances of success. I did some analysis of d20 + score vs. d20 + score. If I remember correctly, Skill Mastery worked out to be effectively about +3 skill points in certain circumstances ... useful at medium levels, but not important at high levels. However, Skill Mastery is great for guaranteeing success in situations where you wouldn't be able to take 10 otherwise: e.g. using Tumble in combat.
For those who say you can't take 10 with Use Magic Device, in Complete Arcane, the Warlock class feature Deceive Item allows precisely this. So it seems WotC designers do intend you to be able to take 10 on Use Magic Device with the appropriate ability (Deceive Item, Skill Mastery); either that or the left hand doesn't know what the right hand is doing.