IMO your build makes it rather obvious that you're thinking about Summon Nature's Ally III a lot. Why not just run with it? It provides a certain degree of versatility, and with your feat selection, will be helpful in every fight. There's your everyday choice. When you know exactly what you're up against, you want to consider more niche selections like the following:
Neutralize Poison (good spell at lower levels actually, where poison is common and dangerous),
Mass Resist Energy (obvious uses),
Heart of Water or Water Breathing (again, obvious, and depending on whether you or the whole party needs to swim around),
Meld Into Stone (ambush scenarios, be-safe option),
Stone Shape (can be very handy in underground locations, or when dealing with stone architecture),
Quench (heavily circumstantial, but when that circumstance comes up, this little spell delivers),
Sleet Storm (best BC available at this level, but maybe also consider Haboob),
Wind Wall (shuts down archers and a variety of breath weapons).