I have too many email accounts, being a web designer and hosting reseller. I use a combination of the Gmail web browser, where I have most of my webmaster accounts forwarded to, and then I use Mozilla Thunderbird for my MacRumors email and then I use the Apple Mail for my more personal friends correspondence. At the office I use Microsoft Outlook for my work email.
Its not as bad as it sounds. Outlook and that account is part of my job and I only use/view it while I'm there.
The rest are personal accounts. Mainly I use the Gmail interface and the Apple Mail. Thunderbird doesn't get used much. I could consolidate them all if I wanted, but I do like using the various clients so as to stay familiar with them in case I can use my experience to assist others.