You could try 'X Resource Graph' which is free. Has lots of other things that it can monitor but you can turn those off if you only want internet speed. Not sure about any others but have a look at www.macupdate.com.
Shop for your Apple, Mac, iPhone and other computer products on Amazon.
We are a participant in the Amazon Services LLC Associates Program, an affiliate program designed to provide a means for us to earn fees by linking to Amazon and affiliated sites.