That goes without saying, right?
Using a free (or AOL-based) email account for business purposes makes you look unprofessional. It’s like when you get those business cards with the message on the back, "Get your own free business cards from…" and then the name of the printer. Smacks of desperation.
However, you could have your firstname.lastname@example.org email forward to one of these accounts, which at least hides your cheapness (most times.) I would instead recommend having your email forwarded to your POP box at your ISP or choose a hosting company that offers POP boxes.
But I digress.
If you’re using Gmail, be sure to read "In Google We Trust."