You should do a search in the forum for apps. I can give you some general advice atleast from my personal experience though:
As far as battery saving, the best advice I can give you is to turn off any auto-syncing that you don't need. I've personally disabled ones like Facebook and my email. I don't want that stuff updating in real time anyways, interfering with my life. I can check email when I want to - I might leave it on when I'm expecting an important email though. Use wi-fi when you're at home. I never bothered to disable GPS, I know many claim that saves battery life, but its only really active when an app activates it.
As far as utility apps go.. I know a lot of people are against task killers, but I've personally thanked mine quite a few times. I use Advanced Task Killer, however, I don't keep it active. I only open it up when I want to force quit a program thats chugging away at resources or is crashed. I also kill the Task Killer itself everytime I do one of these refreshes. Just make sure you have it unchecked for alarm clock or whatever other widgets/apps you don't want killed.
Appbrain and DropBox are both awesome for installing apps from your computer to your device and sending files from your computer to your device.
I also have Volume Toggle that I use on a daily basis that allows me to switch my volume profiles depending on situations (work, home, etc). I have it as a widget so I can change quickly with just one "click" - which leads me to my next suggestion...
For many apps out there, you might also want to test what widgets they come with. For example, I have Astrid for my TODO lists.. however, having it on one of my screens as a widget, creates a mini list visible without having to actively open it as an app. Just nice to have a little reminder when I'm going through my screens.
Other than that.. just do some google searches for apps on what specifically you need. There are so many apps that the list can go on and you really need to test em yourself to find out what you like. I had to test out a buncha camera apps to find out what combination suited me.
