What software outside of your smartphone is integral to your usage of the phone? Besides iTunes, I would say Handbrake because it makes the process of converting DVDs for the iPad so incredibly easy and the results are always great.
iTunes regardless is using android or iOS. MS Office. Dropbox.
TabletTalk (Ok it's a tablet app and there's also a phone component; not sure if it counts).
None in particular... maybe Windows explorer as I use it drag & drop to just about every file. I hate "automatic" programs and I always prefer to create and copy/move all files myself.
Win Explorer for monthly backups off the SD card but other than that no other software really required.