So far, I've used the Shinyei sensor for measuring PM. There are a bunch of other sensors out there, but most are fairly hard to get, at least if you're in Germany like I am. There's one other one that's fairly common and available, the Sharp GP2Y1010AU0F. It's in about the same price range as the Shinyei Sensor from the Grove Kit, so I decided to give this one a try as well.
I once again used a WeMo D1 ESP8266 board as microcontroller. The sensor needs some resistors and stuff, so I added a small breadboard, and lasercut a baseboard so it doesn't look like a bunch of tangled wires. The software setup was similar, the sensor gathered the data, and sent it over WiFi to a webservice.
Unfortunately, the measurements I got didn't really show anything meaningful. If you look at the screenshots above, the top shows the measurements of the Sharp sensor, while the bottom screenshot shows the measurements of the Shinyei sensor during the exact same timeframe. The bottom one also includes temperature and humidity measurements (the test board had no DHT22 on it). As you can see, there are quite a few big spikes in the bottom screenshot, which relate to things I did in the apartment during that time, such as cooking or vacuuming. The Sharp sensor did not show any of these spikes, which seemed unrealistic to me.
Long story short, I decided to stay with the Shinyei sensor. On the long run, I will probably check out other sensors again, but for a first version, I'll just use that.
(Edit: added measurements and some explanations)