Entangle....and (MotW) Briar Web, if you can get it. Even at high levels, Entangle is a mook-buster.
Obscuring Mist is also excellent. I call it my "BAMF!" spell (obscure comic book reference, see Appendix C-2). If your DM throws lots of archer-type bad guys at you, this spell can save your hide.
At 2nd level, the spell use is much more situational. You may never need Resist Energy, for instance....or you might need it "real bad".
The 2nd level druid spell that sees the most use in my game is Flaming Sphere. Summon Swarm back-fired on my PCs pretty badly.