Stanford University
Stanford Encyclopedia of Philosophy: Gottlob Frege
Good summary of Frege's thought. Some sections are more technical, but the explanation of his philosophy of language and other sections are more readable.
Stanford University
Stanford Encyclopedia of Philosophy: Frege's Logic
Lengthy and detailed, but also quite technical, article explaining the major theorems of Frege's logic. Introduction gives a helpful overview and bibliography is included at end, but anyone without a background in logical notation may...