First thing you should do is sign into your google account and sync up your contacts, emails, and calendar. Then you should customize your homescreens to your liking.
Some Recommended Apps/Widgets:
Astro - This is a file explorer app. Android doesn't come with one by default. This is a must have app if you plan to copy/delete/move files on your phone.
Google Maps - you already have this installed, but google recently released a new version that is a lot better.
Launcher Pro Plus - Some people don't like the default launcher(blur). This is a replacement launcher (well it actually just sits on top of blur) that is customizable. There are other ones in market such as golauncher and adw launcher that is worth trying out.
Google Voice - If you have an account, you can set it up as your phone's voice mail and use the app to access your messages visually. You can also acquire a google voice number that you can use to make calls and send/recieve sms messages for free.
Beautiful Widgets - It's a popular clock and weather widget that is customizable
Calendar Widget - I think it's very useful to have a calendar or agenda on your homescreen to keep track of your appointments. There are a lot of them in the market. They all have there pros and cons. Try them out and see which one you like. Two popular ones are pure calendar and android agenda widget. I think Launcher Pro Plus also with a calendar widget
Alarm Clock Plus - a feature rich alarm clock. Much better than stock.