I want to swap information between 2 devices using Modbus/TCP. The 2 devices are on different Ethernet subnets, so I believe I need a router or Layer 3 switch to enable the data from one device to get to the other device and vice versa.

Has anyone installed a similar setup? What networking hardware did you use?

You are correct. If you need the IP addresses of the devices to be on separate subnets, you could use a router or layer 3 switch (functionally the same thing if you don't have complex or widespread requirements). Both would have an interface with an IP address on each subnet/network that would be the "default gateway" for the respective devices. Things get hairy if you already have separate default gateways. Most likely the router would physically plug into two separate ports while the layer 3 switch would have separate VLANs for each subnet with a logical interface on each.

We're talking basic network functionality here. Getting brand specific at that level of detail would be like asking what PLC you like best to do an XIC or XIO.