I came across two apps that I'm betting many people will find useful on their Macs: Milkyway and RapidoStart.
Milkyway (MW) is a small program by Launay Software that previews your image files with a pop-up window that you can resize. I tried this out because of a complaint from my wife. My wife was told me the other day that she couldn't easily preview images by selecting them with a large enough window in the finder. She also didn't really want to use iPhoto (because it's sluggish as hell, in part).
So, recently, MW popped up on MacUpdate with a new version. I kind of remember downloading this in the past, but it didn't work right - but my memory is fuzzy. When it's installed and you start the app, it stays out of sight. You can choose to show the icon in the menubar (way cool) and you can choose to have it start on log-in.
The MW pop up previews can be resized considerably, and you can also move the window wherever you like on your screen for future pop-ups. It also has this 3D glass effect - nice touch - that you can choose to disable if it's annoying. Give MW a try! I like it, and it's just unobtrusive enough to like.
The other free app I think many of you will like is RapidoStart, by App4Mac - makers of some other free apps with the "Rapido" prefix, like "RapidoWrite". [Note - I sort of recall that this RapidoWrite was shareware at one point - got a note from the developer once. Maybe it didn't sell well.] App4Mac also makes other apps in the shareware or commercial category as well.
RapidoStart (RS) was updated recently and caught my eye in a discussion about uses with QuickSilver. RS is essentially a supplemental dock you can call up when you need it by clicking on a small green tab in the corner - or with a key-command. The pop-up dock is customizable; you can add what ever apps or files you want and even make several sets of things for different purposes (e.g., image manipulation apps, PDF apps, research project docs). For those that don't like the non-visual nature of QuickSilver, it provides a visual way to get at apps you don't have room for on the doc. And if you are someone like me, with many apps I use for different purposes (and you can't remember the names) - RS seems like a great way to get to these apps. Unlike Quicksilver, which learns your patterns and sets up the keyboard shortcuts, you'll have to customize RS your self for the files you want to access.
The pop-up window is gorgeous - well rendered, and the app is very solid. Give it a shot and see if it helps your work flow.