Gelzer's book on Caesar is available in English, unlike his book on Cicero which has never been translated from German. Both are excellent. Meier also has a book on Caesar which I think is somewhat less good, partly because he contains no citations (or at least my copy doesn't). There's also Goldsworthy's book but frankly, despite the frequency with which it is recommended, I really don't think it's very good--Goldsworthy makes quite a lot of errors, particularly regarding political matters (he's a military historian, after all, so I don't hold it against him). It's a fairly good introduction to the material, and very readable, but many of his errors on political matters are kind of elementary or very simplistic. And of course there's the textual source material as well

The Life of Caesar Podcast. They've moved on to Augustus now but there are almost 50 episodes about Julius.

Here's the In Our Time podcast on him. A good way of getting an overview as it's only ~40 mins.

Caesar's own Commentaries are good reading. They might be available in audiobook format.