I have tried lots of aps. Honestly they are all really buggy and less than ideal but the livestrong ap is the best. It has the largest food database and works at least 80% of the time. I use it on iphone & the tie-in website on my pc.
I'm going to echo everyone's thoughts on here and say how much I love Myfitnesspal. It's taught me to be a food diary-keeper, and I never would have done that before. Now I always factor it in my thoughts when deciding if I should eat something or not, since I know I'll have to make record of it. I love how it keeps me on track!
I'm just starting with the Livestrong blackberry app. I had trouble downloading the app, I had to call my wireless carrier's customer support but it works now. Livestrong's calorie counting app costs $3 I think or right around there. On your blackberry, make sure your WiFi is off when you download the app, since my WiFi was on, that's why it didn't originally download. I find that Livestrong isn't 100% accurate with the nutritional info they have stored in their database, but they are pretty close.