I have two servers that I want to place in a collocated facility but I
need to select a device (a managed switch I believe) to place in front
of the servers to protect them from hacking attempts and route the
appropriate traffic to the right machines based on IP and port.

I only need 4 Lan ports and 1 wan port. 

The setup will be something like the following:

Live Server (Win OS)
Dev  Server (Win OS)

Many Public IP's to the router through one ethernet cable. 

I need to route the traffic through the device based on port and IP combined.

This device would also need to be very stable and have good
connectivity on the local network (gigabit) since the servers transfer
a lot of data amongst each other.

Simplicity of interface is also going to be a concern since I'm a
programmer and not a networking guru. I can handle setting up routing
tables on a very basic level but anything CISCO is going to be out.

Cost is also another factor. My spending range for this device should
not exceed $400.00.

I would prefer a smaller device so that I don't get charged for space
from the co-lo company (not something that is rack mountable).

Thanks for your help!

James

Here are some inexpensive all-in-one boxes that appear to meet your requirements:

http://www.netgear.com/products/details/FVS124G.php
http://www.dlink.ca/datasheets/DGL-4100_ds.pdf
The Linksys RV0041 looks like it would also qualify but it looks like
the website uses session linking so no direct link.

However if this is going to be a high-bandwidth site you may need to
separate the switching/routing/firewall functions. Also depending on
the data on the servers you might want to consider bringing in an
experienced person to configure the firewall to make sure you don't
have any holes.