One of the bad things about being a procrastinator and putting off doing this post: some of my most used apps have already been covered. I'm going to need you guys to all pretend you didn't already read Adam, Bla1ze, Ryan, or Joseph's lists and it will all seem new. Lots of people complain that BlackBerry just doesn't have any apps, and while we are missing some that would be nice to have, I think there are plenty out there to make use of.

In no particular order, my most used BlackBerry apps are:

SocialScope
Aside from email, I spend the most amount of time on my BlackBerry in SocialScope. It combines all of your social networks into one easy-to-use and visually awesome app with lots of customization options available (font size, color themes, etc). You have the option of using SocialScope for Twitter, Facebook, foursquare, and Flickr - though I admit I use it just for Twitter. This is the only Twitter app I will use on my BlackBerry, and it's been that way for over 2 years now. The only downside: it's in eternal beta status, and invite only. One of my wishes for the CrackBerry nation for 2012 is that SocialScope will finally release for everyone! In the meantime, you can request an invite from a friend or stranger for that matter, and sign up for the beta program at the link below.
Sign up for the SocialScope beta

BerryWeather (aka BeWeather)
A weather app is a must for most smartphone users, regardless of your platform. My favorite is BerryWeather, for all of its functionality and the ability to customize the heck out of it. The forecasts seem to be accurate (or as accurate as any weather forecast ever is) and I like that I can see the temperature in my notification bar. Another favorite function is the ability to add multiple cities so that with a quick swipe I can see if Bla1ze is about to get swept away in a hurricane up in Nova Scotia. You can download a free version of BeWeather or splurge and get the premium version for $9.99.
More information/download BeWeather free
More information/purchase BeWeather premium

InstaPhoto
I take a ton of pictures with my BlackBerry. No really, a ton. While the BlackBerry Bold 9900 has kind of put a damper on the quality of pictures, there are apps out there that can help that appear less obvious and add some fun to your shots. InstaPhoto is one of these apps. It's sort of like Instagram (that super popular iOS app), with filters and frames you can add to your photos, and options to share the results via Twitter, Facebook, and email. It's pretty fun, and available for both the BlackBerry PlayBook and most BlackBerry smartphones. You can grab InstaPhoto for $2.99 at the link below.
More information/purchase InstaPhoto

foursquare
I mentioned earlier that you can add your foursquare account to SocialScope, but I'm kind of weird and like to keep them separate. That's where the foursquare app for BlackBerry comes in. This app has seen a lot of updates over the past year, and I think it's gotten better over time. The UI is fun and easy to use, and it's great to be able to check in wherever you go and see available specials around you. If you're in to location based services (LBS) such as foursquare then you likely already know about the app. However, if you see your friends checking in to all these different apps, and don't know where to start, foursquare is a good basic LBS to get started with. The foursquare app is free and available at the link below.
More information/download foursquare for BlackBerry

Leave It On
Leave It On is one of those apps that once you have it installed, you wonder why it wasn't just built right in to the OS in the first place. This set-it-and-forget-it utility displays a pop-up message for any number of different apps (email, BBM, SMS, IM programs, Twitter programs, and more) which you can customize in all sorts of ways. It also has a backlight feature (hence the name, right?) that will keep your BlackBerry screen lit while you're using applications that you designate which is super handy for apps like maps and the media player. You can snag the free version of Leave It on, but to get all the features you'll want to go with the premium version. If you prefer to try before you buy, the premium version comes with a fully functioning free trial and costs $2.99 after that.
More information/download Leave It On free
More information/purchase Leave It On (with free trial)

GetGlue
I decided to throw in an extra app since a few of mine were already covered by the other writers. GetGlue is another social networking app, but instead of sharing where you are, you check in to movies, TV shows, books, music, food, topics.. just about anything you can think of. This one comes with rewards though, because some check-ins earn you stickers, which (unlike foursquare badges) you can request physical copies of for free! It's strangely fun to use, and a great way to discover new shows, music, and topics that you might otherwise not have found. The GetGlue app for BlackBerry is decent, but unfortunately is no longer being developed for. You can still download and use it though, and it works great for me. There's even a sticker for using the BlackBerry app to check in. The app is totally free and can be found at the link below.
More information/download GetGlue

In closing, I wanted to mention that all screenshots were taken with Capture It, though I am also a fan of ZonaSnap. If you don't have a screen capture utility on your BlackBerry, you're missing out. They come in super handy for all sorts of reasons!