You can create multiple email ids on yahoo, and all the emails will end up in the same email address. To create more yahoo ids goto http://edit.yahoo.com/config/list_alias?.src=ym
Log into your primary email account and you can create more email ids. All the mails will go into your primary account. So if you are stuck with firstname.lastname@example.org you can finally change it to email@example.com
All your mails will still land into firstname.lastname@example.org but you can give out a better looking email address.
I saw this last year and somehow forgot the URL. This post is more of a bookmark for myself.