Provide us with a little more info and we may be able to offer better suggestions. Let's start with this, would this be a home base system or mobile? Also what do you ultimately want to do with your system? If it's a base system then do you want to be able to upload data to a web site or just track it for your own purposes? If it's a mobile site (like in your car) then what kind of data do you want to capture? Will you also use a laptop with it in the car? Stuff like that will help us in our suggestions.
Personally, I'm envious of you for having the Davis already. All I have is a cheapy Natl. Geographic model. The Vantage Pro 2 is a sweet system and I wouldn't complain about having one. I'm slowly in the process of saving up for a new Pro 2 system but I'm not that great with saving.
It would be my base system as I would like to grab the data from it and be able to post it on a web page.
Recently I discovered a company called Peet Bros.
whom have some really nice systems as well. Their interface is smaller than the others and you have to toggle through the different screens but for a mobile application I think it would be perfect. It's not very big and would fit on a dashboard perfectly without taking up a lot of space. Plus you can download the data to a computer.
I hope this helps some.