I don't see any evidence of 3.5 power creep, except perhaps in monsters.
My definition of power creep is:
a) New material regularly exceeds the upper limits set by older material, and each subsequent release raises the bar further.
OR
b) New material is significantly more powerful on average than older material, and each subsequent release increases the average to remain ahead of the curve.
3.5 doesn't meet either criteria in any meaningful way. It has a few areas of creep in b), but mostly in the sense of flattening the power curve out rather than bending it further.
CORE CLASSES
a) None of the core classes in the Complete books are as good as the best in the PHB, so they aren't raising the bar. Eberron's artificer is strong, but not as good as a druid or cleric. Nor are the Complete Adventurer classes better than (or even equal to) those in, say, Complete Divine. No creep.
b) Since there's a higher percentage of primary spellcasters in the Completes, their average is higher than the PHB's, but their average for any of the three primary archetypes (warrior, spellcaster, expert) is lower. Similarly, Eberron has a higher 'average' since its one base class is near the top. But, it hasn't followed up with additional above-average base classes. No creep.
PRESTIGE CLASSES
a) The best PrC in the DMG is probably the Archmage, although you could make a case for some of the others. The Hulking Hurler tops that, as does the Ur Priest. Evidence of DMG-Warrior-Divine bar raising. However, the bar lowered to DMG or sub-DMG levels with Arcane and Adventurer. Possible creep, but quickly corrected.
b) The average PrCs in the supplements are dragged down considerably by classes that would be sub-par in the first 10 character levels, still more when you actually have to qualify for them. Overall, the supplemental PrCs have a lower average. The warrior types are much better but still sub-par by the time they become available. No creep.
FEATS
a) The most powerful feat in the PHB is Natural Spell; its better than most very strong PrCs' capstone abilities. Combat Reflexes and Power Attack are probably 3. and 2., respectively. Nothing in the supplements comes close to natural spell, nor is their a visible trend toward feats stronger than CR or PA. No creep.
b) The average feat is probably a bit better, if only because the sub-par +2/+2 feats are largely absent. Creep, but slight and probably more balancing than not.
RACES
a) Dwarves are the most powerful PHB race; one could argue till the sun goes down (unless it is down in your area) what the best MM one is. Warforged and Goliaths are about the only really good races intended for PC use, and I don't see either as equal or better than dwarves. Because of monster creep, there may be slight monstrous race improvements, but considering the ruthless LAs, probably not. No meaningful creep.
b) The average in races is definitely better. WotC doesn't print substandard races like half-orc anymore; all the Eberron, XPH and Complete races are at or above the average. Definite creep here, but on a small scale.
MONSTER CREEP
a) Now we're talking. There are some absolutely brutal monsters out there who seem way undercosted for their CR. MM3 is definitely more powerful than MM1, with the exception of dragons who were already outrageous for their CRs. Definite creep, but not enough evidence to see if it will get worse.
b) Even worse than a) - the average of MM3 is closer to the upper tier of MM1. Massive creep, but no pattern yet.