I really like James's solution above, and have something similar set-up myself, but there are still some issues if the e-mail addresses you want people to see are NOT gmail.com accounts.
I have a personal domain @adrian.co.uk which is hosted by Madasafish. I've had this for over 15 years and this is my main personal e-mail address
I also have a company domain @company.co.uk which is hosted by Pickaweb. I've not had this long, but had a previous company e-mail through Pickaweb for 9 years
Both provide a mail forwarding service, which is use to forward to my me@me.com account, which I've been using since switching across to the Mac 4/5 years ago. This means that all e-mail I receive ends up in me@me.com and pushes out to all by iDevices
The issue I have is being able to send e-mails from @adrian.co.uk or @company.co.uk and the only free solution I've found is using gmail.
I have two gmail.com accounts - personal@gmail.com and company@gmail.com.
In the gmail settings (Accounts and Import) it's possible to add an e-mail address to "send mail as" so in my personal@gmail.com I add @adrian.co.uk and in my company@gmail.com I add @company.co.uk
Just in case anyone replies to the @gmail.com accounts, I also have both accounts forwarding mail to my me@me.com account.
In Mail I have 3 accounts. My me@me.com account for sending and receiving (so I can send from me@me.com if I want, and I even have an iCloud alias to send from company@me.com!) and 2 gmail accounts - personal and company - which are just used for sending from @adrian.co.uk and @company.co.uk.
The only issue with this solution is that mail received using the "send mail as" accounts is displayed as "adrian [personal@gmail.com] on behalf of adrian [@adrian.co.uk]" or "adrian [company@gmail.com] on behalf of adrian [@company.co.uk]" Replies to these e-mails goes back to the correct accounts (i.e. not back through gmail) and is then forwarded to me@me.com, but it would be nice if I didn't have the "on behalf of" details in the address.
The solution works, and means I can receive and send mail from any iDevices but it would be much cleaner if you could just use iCloud SMTP to send mail with another domain name!