My first email address followed the convention of initials+nickname. And since my boss chose it for me, she picked the nickname she loved calling me the most (especially when she had a problem, no clue what to do, and needed someone that could think creatively, fast, and stay within the budget)
alrknowitall
Of course you could use a descriptive word that gives some clue of what you do, like initials+occupation or a topic you are really into that looks good on a professional email. Something like ABC+Developer or DEF+Art, GHI+Finance, or in the case of my daughter who has the coolest initials for someone into photography, SLR+Photography. The added bonus is that many combos like this can also be suitable company names, if ever you decide to go that route in the future. (very similar to what rgdot suggested)