If you're going to be in sales, I believe you should look like it every chance you get - including when you are using your email. Save the inventive names associated with your yahoo, hotmail, msn, gmail, aol, and other accounts for personal use or when you are trying to maintain some level of privacy or anonymity.
Unless you are known by your nickname and it appears on your business cards, it should not appear anywhere in your email address.
Let's look for a second at why you send someone an email - to have it opened and to have your message read. Two inherent issues here: (1) the intended recipient has to get it, meaning that it has to get past the spam or junk filter and (2) they have to open it and read it, which stands a greater chance of happening if they recognize who is sending it.
I'm not saying you shouldn't have a yahoo, gmail, hotmail, aol, msn, or other account. I'm not saying that at all. However, compare "email@example.com" with "firstname.lastname@example.org." In the first instance you (or my customer) might not recognize or know who it's from. In the second it's identifable as a business email.
Now, you may not have a company domain or website to use as part of your email address. If this is the case, use your whole name (first and last) or the name of your company with the public email address. If you have a registered domain name, use that in your email - people will more easily understand who it is from and you'll get another opportunity to brand your company or community.