"Just Pictures" is also very nice. It has some other functionality and can display pictures from a number of sources. It doesn't scroll quite as fast as 3d Gallery but the thumbnails are larger. JustPictures! - Android app on AppBrain
I've been uploading my photos to Picasa and Photobucket Pro and using the photo gallery that comes with the app. So far I've been liking Picasa a lot as I can do the organzining on my computer then uploading it to the website and later view on my Incredible. Any photos that I keep on my phone is view via the OEM photo viewer. I don't like to keep photos on my phone's memory or SD card as these files does take up a bit of space.