Main Page:
Add some CSS to the "Sign Up" button (And possibly the input box). Everything else is themed, and the button looks odd as is.
Also, when a user clicks in the input box, you may want to have the text disappear so they don't need to highlight and delete.
Code:
<input type="text" size="15" value="Enter Email" name="email" id="email" onclick="if (this.value=='Enter Email') this.value='';" />
Also, if you're running a "Professional" site, I would try to remove the "lol"s, slang, and other unprofessional content.
Sell Domains:
You're trying to get people to sell you their domain names. Professionalism.
I've always considered "CA$H" to be something a 13 year old might write.
Consider the use of the words "I" and "We". If people are selling domains to your website, they may feel better at least thinking it is more than just some back alley site build by One guy. The use of "We" might convince them there is a team behind it. Obviously, they aren't going to think of this step by step. However, subconsciously, it could help influence them. You have "About Us", but it's really just about "You". You might was to get your story straight before selling it to us

Possibly replace the word "quick" with "timely"
Add some CSS to the input button, make it a little wider.
Contact Page:
Again, the submit button needs some CSS.
"CC yourself on message" can be confusing.
Maybe say "Send a copy of this message to Me", but "CC" is pretty vague. Granted, people selling you domains probably have internet experience; however, you'd be surprised at the stupidity you'll run into.
My biggest pet peeve: Terrible "CAPTCHA"s.
What is the sum of 22 and 8?
The point of a human test is something humans can solve, but computers cannot. The last time I checked, computers were Better than humans at adding. In my opinion, if you're going to use something that a spammer can bypass in about 2 extra minutes of coding, you might as well not use it at all. The fact you're using something so easy to break is likely to attract more spammers, many who just want to make their point.
Domain VIP List
CSS on button.
Maybe spread the rows out vertically a little bit. I feel cramped.
Also, if they didn't have a real email (eg, just left 'Enter Email' in the box and submitted sign up), don't have that appear in the email box.
That was really all I picked up. They're just suggestions; I'm more of a "programmer" than a "Design Guru", so feel free to ignore anything.
Bruce