I've been playing again with Google ngram, which shows the frequency by which words appear in books that are in the Google database, normalized to the number of books. Here are some keywords from physics that I tried which I found quite interesting.
In the first graph below you see "black hole" in blue which peaks around 2002, "big bang" in red which peaks around 2000, "quantization" in green which peaks to my puzzlement around 1995, and "dark matter" in yellow which might peak or plateau around 2000. Data is shown from 1920 to 2008. Click to enlarge.
In the second graph below you see the keywords "multiverse" in blue, which increases since about 1995 but interestingly seems to have been around much before that, "grand unification" in yellow which peaks in the mid 80s and is in decline since, "theory of everything" in green which plateaus around 2000, and "dark energy" in red which appears in the late 90s and is still sharply increasing. Data is shown from 1960 to 2008. Click to enlarge.
This third figure shows "supersymmetry" in blue which peaks around 1985 and 2001, "quantum gravity" in red which might or might not have plateaued, and "string theory" in green which seems to have decoupled from supersymmetry in early 2002 and avoided to drop. Data is shown from 1970 to 2008.
A graph that got so many more hits it wasn't useful to plot it with the others: "emergence" which peaked in the late 90s. Data is shown from 1900 to 2008.
More topics of the past: "cosmic rays" in blue which was hot in the 1960s, "quarks" in green which peaks in the mid 90s, and "neutrinos" in red peak around 1990. Data is shown from 1920 to 2008.
Even quantum computing seems to have maxed (data is shown from 1985 to 2008).
So, well, then what's hot these days? See below "cold atoms" in blue, "quantum criticality" in red and "qbit" in green. Data is shown from 1970 to 2008.
So, condensed matter and cosmology seem to be the wave of the future, while particle physics is in the decline and quantum gravity doesn't really know where to go. Feel free to leave your interpretation in the comments!