What I would do after some Hitchcock is check out these two:
The Maltese Falcon
The Asphalt Jungle
(also Double Indemnity, which someone mentioned above)
See how you feel about those. If you enjoy them, then you have the entire canon of film noir to look forward to, which is brilliant because even the shit films in the Golden Age of that genre (1940-1959) are cool as hell.
Also, you have to watch Casablanca: a brilliant love story, suspense film, war film, mystery ... it is everything. Which reminds me that you have the entire catalogue of WW2 films to watch, like "Hell is for Heroes" and "The Longest Day" and "A Bridge Too Far."
Honestly, we could make lists for you that are 10 miles long and would just confuse you to death haha