I am also really happy with my research group composition right now. I have a really nice bunch of graduate students and they are all really smart. I have been really enjoying the the group meetings, hearing them present, and the "guided reading" course that I am offering to a few of them -- it has been so much fun! Interactions with students are always an efficient way to lift my mood.
1) Brainstorming/troubleshooting with my graduate students. Listening to two graduate students try to find their way out of being stuck. These are the best times, because they show you how much the students have grown and how much they can do on their own. As a junior faculty, I used to get frustrated when people got stuck, now I am just so excited for them because of all the awesome that is waiting on the other side of that dam that is just about to burst...
2) Hearing that the department is working on my next promotion.
3) Writing papers. It's a favorite every week. It may be my absolute favorite part of the job altogether.
4) Heck, all of writing. I even like writing grants and responses to referees.
5) My quiet, huge, early-ish class, finally warming up and speaking up. Heads are nodding, there is even spark in some eyes. Could also be contacts.
6) Colleagues listening to what I have to say; appearing to respect me in a leadership role.
7) My office. I have the best office in the world. It is large, with high ceilings, and delightfully messy.
What do you love about your job?