One of my favorite things on my phone is the widgets -- the apps that run on the home screen.
Here are the ones I usually run on my home screen, though I swap in and out a lot:
Beautiful Widgets (Clock & Weather, also comes with some nice power toggles)
Financisto (Quickly view my checkbook balance)
Handcent SMS (see how many texts I have if I haven't checked in a while... such as at work)
Battery Left (an estimate of how much is left on your battery, in percentage (by single digits) and time)
Facebook (check on some friends' status updates with a quick glance)
Sportstap (scoreboard app, imperfect but apparently the best we've got right now)
CalWidget (LOVE this app. Have different calenders -- one for general dates, one with the schedule of games I'm working for MLB, and another with the Yankees schedule)
SlideShow (cycles through pictures in a folder)
What widgets do you have and love? I'm always looking for stuff I'll like but haven't heard of yet.