How much Hemingway have you read? The Sun Also Rises is definitely worth reading if you liked The Old Man and the Sea. Farewell to Arms as well, perhaps. EDIT: You might want to look up some Conrad and Graham Greene, as well (The Quiet American comes to mind, as does The Power and the Glory).
Oh my gosh, I didn't even see this post and as I was scouring the net for Hemingway, I downloaded both Farewell to Arms and Sun Also Rises. Big coincidence? Perhaps not. The Old Man and the Sea is the first Hemingway I've read I think, if you discount Hills Like White Elephants (good old English class). Is For Whom the Bell Tolls good? I didn't have the chance to read that in English class.
I personally had a hard time with For Whom the Bell Tolls, though it's also one of the more popular Hemingway books. It certainly has more plot/'action' than The Old Man and the Sea or The Sun Also Rises (in this I'd say it's more similar to Farewell to Arms), but I found that its length caused me to get quite tired of the (typically Hemingwayan) protagonist by the end. Your experience may be quite different from mine, though.