I was interested to see some people say they've commonly heard it pronounced as a single syllable. I've heard that, but I didn't know it was common.

Here's a website with an audio clip of that pronunciation (http://inogolo.com/pronunciation/Graham)

Here's a website that has many pronunciations. (http://www.forvo.com/search/graham)

The Forvo website is interesting because it has some American (?) accents using the 2 syllable form, and some (Lindsey Graham) using the single syllable form.

(DuckDuckGo's search results were particularly useful for me here.)