Your iPhone 3G or 3GS is just as much an internet device as it is a cell phone. With this we are intended to unite the two worlds of communication in a single Zeitgeist for cross platform access. Because of this you are able to unite the internet options you have on your home computer with what you have on your mobile.
Sync Your Bookmarks
Bookmarks are commonly used, but get scattered between using multiple browsers and different devices. The best way to keep them all organized and recorded is to sync them with your iPhone. When you have your iPhone plugged into your PC go ahead and open iTunes and go to the left hand panel and select your iPhone. Click on the Info tab and go down to the Web Browser section. Click on the box there to make sure that it is going to sync the bookmarks. In the pull down menu there are usually only two browsers at default, Internet Explorer and Safari. No matter which one you select it is likely going to sync the bookmarks from every browser you use. Once you make sure that the box is checked there and down in the Advanced section you can go ahead and sync your iPhone again. Once it is done open Safari on your iPhone and you will see that in the Bookmark menu you will have bookmarks for all of the browsers you used on your computer.
Syncing Email Contacts
The same thing can be done with your contacts from you email account, depending on what service you are using. iTunes openly supports Windows, Google, Yahoo, and of course Outlook. This can be difficult unless you have already opened your email address list. The best way to do this is to connect Outlook to your existing email address and then sync Outlook with your iPhone. You may want to avoid this unless you do a large number of emails from your phone. If you are going to do it make sure that you do not have an overly crowded contact list. The process is exactly the same, with making sure the box is checked and then doing a standard sync.
Using Mobile Me
If you feel like doing an extensive amount of internet coordination you may want to consider a Mobile Me subscription. Remember, this costs money, but may be effective for your needs.