1. Logic
Does the name make sense for your product or business? Obviously this isn't a hard and fast rule as there are exceptions of companies with strange names that are unrelated to their actual business that have succeeded such as delicious, flickr, etc. Additionally, there are some names that very loosely related such as Google (math) and Yahoo (feeling of excitement), but are still basically nonsense words.

2. Length
The shorter the better, but don't be so focused on length that you change it a bizarre name that doesn't make sense like frtb.com. Additionally, a one word name is usually easier/better than two or three word name.

3. Spelling
Once again there are examples of companies with misspelled names that have succeeded (Digg, Flickr), but why add this additional hurdle? How many people hear about Digg and Flickr from a friend and go type in dig.com or flicker.com? That's lost traffic you may never get back.

4. Domain extensions
You'll also want to try and acquire as many of the other domain extensions besides .com. These include .net, .org, .info, .biz, .ws, .me., .io, .us, and if you are going to be global and have sites in other countries you should consider those as well. If you can't acquire the .com, I'd recommend finding a name where you can find it instead. Once again, there are a few examples of companies like del.icio.us that managed to succeed, but note that they did buy the domain name delicious.com when they had enough money to pay the price later on.

5. Ability to pivot
Many companies end up changing their business model dramatically during their life. If your name is too specific to one particular model, it may constrain you from pivoting to the right model later on.

6. Don't be too generic
All the above advice would seem to point people to a simple one word name. While this can be great if you can secure such a domain name and also not have trademark issues, there can be a downside to your name not having any personality or not being memorable if it's too boring. Luckily, unless you're willing to write a huge check to acquire a short one word name, you'll have to compromise on one of the categories above.

The bottom line is that naming is tricky without having to worry about a domain name as well. Combine the two of them, and you've got a difficult challenge that requires significant thought and research.