Type: Logo or something like that
Text: ARRIBA the one and only - sponsored by Ambrosia --- (try to fit what is important: ARRIBA and Ambrosia must be there)
Colors: What looks best, probably blue and orange should be in there somewhere...
Size: 700x600 (or something close to that, so it can attract many players)
Materials:
http://awdawdawdd2.comyr.com/ -- the logo in the middle.
Comments: So, basically a logo that I just showed looks good but it needs something... That something may be a good background. In our server there are at least 8 different types of game-modes. Placing them in one image may be a little tricky. I tried that once myself, but it didn't look pretty.

As you can see that, the GTA San Andreas characters are separated by those black thick lines. That would be actually a great idea to place all those images of the modes together.
Here is the link for those images:
http://awdawdawdd2.comyr.com/images/pics/1.png -- go from 1.png to 12.png
Moreover, look at this link:
http://imageshack.com/i/nra5ulp - It has many images that I have uploaded.
Now, I know this is a tough job but it would really be worth it. It would really attract players when the server is advertised.