You are able to find a lot of useful applications for your device via the Android Market. I will advise that if you download an applications that causes issues with your device such as viruses or malware, Verizon Wireless is not responsible for the damages done.
I downloaded Handcent SMS, which is a texting ap and I use that as my default now. I was annoyed that our text feature doesn't turn on your screen to alert you that you have a message when the phone is on silent...but Handcent comes with a notification pop-up feature that will turn on your screen and alert you. So, if you like that, it's a good ap to get. Also, it's kind of fun since that ap will also let you change the colors of your text messages, and themes to make it look like an iPhone.
I also downloaded Advanced Task Killer. It tells you which aps are running in the background that you don't even know about, and will shut them off for you if you select that option. It's been very useful in help saving my battery.