I'll admit I had a little difficulty navigating this site. When searching for land patents on the Maryland State Archives website, I found it easier to do an "advanced" search and enter in the last name I was looking for. Not the easiest way, but I did find entries for people for whom I was looking.
This link takes you to the Harford County section--just click on "advanced search" to perform a search or scroll to the bottom and click on the county you need.
We'll try and keep incorporating new sites into our tips--chances are that not every one will apply to you, but we'll try and keep them varied.