With Google now predicting as you type, I thought it would be interesting to see what comes up after one letter. This is for an Australian search, I am having a guess when I say that I think that it would be based on traffic to these websites as opposed to SEO (I looked at Google Insights on search traffic but that did not support the findings). It is interesting to see that Lasoo got up there for the letter 'L' it would suggest that you should probably look for a starting letter with not much competition if you were choosing a brand name which obviously would have low awareness.
A - ANZ
B -BOM Bureau of Meteorology
N-Netbank (Commonwealth Bank)
O - Optus
R-RTA (Road and Traffic Authority)
U-UAC - University Admission Centre
Z -Zmail - UNSW Email