In another users answer http://chinese.stackexchange.com/a/2046/38 they said:
一 is pronounced in the first tone when it stands alone. It is pronounced in the fourth tone when it precedes a first, second, or third tone. However, it is pronounced in the second tone when it precedes a fourth tone.
I was surprised to read this and didn't believe it. However, when searching the net I found several places where this is mentioned.
I checked Google translate and it gave me Yīzǎo for 一早 and Yī nián yǐhòu for 一年以后 which is what I always thought it was.
A search on Google for "yīnián" provides me with 106,000 results, but a search for "yìnián" only provides 6,330 results.
Obviously, the examples above only provide partial evidence of correctness. But, is there a reliable, authoritative resource which can confirm the claim that 一 should change to 4th tone?