Aside from a blood test from the Doc, Clearblue is pretty much the best you can get.
With my first, i tested 2 days before my period was due, as I was leaving on a trip, and it was negative.
7 days later I found myself in the middle of Borneo, still no period, no way of retesting, and morning sickness kicking in.
By the time I got back to KL it was obvious I was pregnant, and I barely had to wet the test and a blue cross came up as bright as can be.
Must say it was a bit of an anti-climax.
I think the phenomenom of finding out so early is a very new one, if we had the patience to wait a few more days we would all get far less negatives!