First thing I would suggest is different logo and use of the large header space up there.
Viewing it right now, the advertisement is white and clashes uncomfortably with the white logo, which is viewed against a bright green header. It's hard to read, hard to see what the site is about. I'd go full length logo/header.
You should do up a quick custom favicon, it can be done with free tools online and just takes a minute, helps your site stand out - right now I see what looks like a JustHost favicon. It's a little thing but it's the little things.
Maybe don't go with an ad under the header - at least at first. It's distracting, it's not centered, just doesn't seem reasonable quite yet. Draw people in first.