Software Toolbox should start paying me...
Check out the
OPC Datahub from Software toolbox to log PLC data to Excel. You will need an OPC Server (RSLinx, Kepware, etc) for most viable solutions.
I wouldn't recommend trying to cook up a DDE->Excel datalogger unless your time isn't worth anything.
All that said, Microsoft Excel is an amazing tool, but it's not the right one for data logging. For that (in the MS world) you would use Access or SQL Server. It's all about storing your data in (SQL) databases not spreadsheets. Spreadsheets can be good tools to work on views of some of the data, but aren't meant for, or good at, dealing with lots of data.
If you expect your project to grow, particularly if you want to access the data remotely, view graphs, generate reports, query the data in any way, etc, you'll be moving more toward what the industry refers to as a Historian. For that you'll want to look into
FactorySQL and
FactoryPMI.
I got in a debate with another poster about this exact topic
here. I'd recommend doing a search. There are lots of posts that address this exact question.