In no particular order:
1. Boogie Nights - great in his small role
2. The Big Lebowski - everyone steals scenes in that film, but PSH is so good with his uncomfortable laughing
3. Magnolia - Of all the powerhouse performances in this ensemble cast, Hoffman is by far the strongest
4. Punch Drunk Love - The only film where Adam Sandler is tolerable. Hoffman is phenomenal, as usual.
5. Red Dragon - Very underrated film. Hoffman is largely ignored, but worth watching anyway, especially due to Ralph Fiennes' performance.
6. 25th Hour - I only like 2 Spike Lee movies. Not surprisingly, he didn't write either of them.
7. Cold Mountain - I was surprised by how much I liked this movie. Hoffman's role is secondary and largely forgettable.
8. Charlie Wilson's War - I need to watch this again, because all I remember was how terrific Hoffman was.
9. The Savages - Haven't seen it, but heard it was really good.
10. Doubt - I'd say it's worth watching. I liked it, but I don't think I'd watch it again.
11.The Master - Ridiculously underrated.
I didn't like The Talented Mr. Ripley, so I personally wouldn't recommend it. As for a "fluff" film, he was really good in Mission Impossible 3, although the movie was "meh", at best. Haven't seen A Most Wanted Man yet, but that is on my list to see.
DO NOT WATCH "Synecdoche, New York." I love PSH and Catherine Keener, but this film is 2 hours of Charlie Kaufman patting his back as he sucks his own d*ck. The most pretentious garbage I have ever had the displeasure of sitting through.