Great primer on the topic via DailyBlogTips…
But here are the main points…
1) They are Short
The shorter the better. Under 10 characters if you can, definitely under 20. The more letters, the more potential spelling errors and typos somebody will make when entering your domain name into their browser. Also, think about your corporate stationery: how is firstname.lastname@example.org going to look on a business card?
2) They are Easy to Remember
Yahoo. Google. MSN. Amazon. Brevity is the soul of memorability.
3) They are Easy to Spell
But brevity and memorability aren’t enough on their own. In general, acronyms are out but so are commonly misspelled words like accommodate, independent, personnel. If your current domain is prone to misspelling, an inexpensive workaround is to register the most common variants and wire them to your Web site. So, for something like accommodate.com, you’d also register acommodate.com and acomodate.com.
BTW, points 1, 2 and 3 are also well worth considering when developing a company name.
4) They have a .COM Extension
I used to have a .NET domain name. Regularly, clients would ask why I hadn’t replied to an e-mail they’d sent a day or two ago. It almost always turned out they’d sent an e-mail to my_old_domain.COM. It’s one of the reasons I switched company names: just to get a .COM domain name. People automatically append .COM to any domain they try to remember.
5) They are Descriptive
If you only have 20 characters to make yourself understood, they’d better be the right 20 characters. If you’re searching for a movie review and Google gives you two sites to choose from—MikesLair.com and MoviesCentral.com—which would you click on?
6) Or they are Brandable
Without getting all Web 2.0 about it, a short domain with an interesting pronunciation can work very well. Good examples might be zaddy.com, neno.com, and todal.com—each of which, if you have a bit of lolly to throw down, is currently available at hugedomains.com for upwards of $24,500.
7) They don’t Contain Hyphens or Numbers
The problem with numbers is that you end up having conversations like this: “No, that’s the numeral 1, not oh en ee.” If your current domain has numerals or dashes, again, it might make good sense to register the most obvious variants. Something like 1-800-flower-pots.com can be backed up with 1800flowerpots.com.