Its not so much the strength of each finger, than the ability to strike each key with the same velocity such that each note sounds at the same volume as each other.
The thumb (not any other finger) is the part most at fault, and is evident in many people when they play scales at a beginner level. Try listening at the point where the RH thumb strikes notes 1 and 4 of a scale. Usually you'll hear a very distinctive "Beat". The objective here is to practice the passing of the thumb with such efficiency that such a beat is minimised, and perhaps even removed. The other fingers usually do not have this particular "feature"
I am currently looking at particular exercises from Liszt Technical Exercises, regarding scales. The first book (which i wouldn't touch) consists of 40 exercises, each dedicated to a particular finger, or a set of fingers. (1 2 3 4 5 12 23 34 45 13 24 35 etc) but the other books are dedicated to a particular branch of technique. scales, thirds/6ths, double notes, chords octaves etc. You might find it useful. I, for one, am looking at the scales exercises.
I also currently downloaded Gyorgy Sandor's commentary on piano playing on this site. You might find the early chapters insightful as well, as he talks extensively on the arm mechanism relating to sound production, as well as many myths about playing.