A lot of great developers don't have the financial resources to flood the market with ads. While sources like Twitter and the App Store have made it much easier to discover new software it's still easy to miss out on something you didn't even know you needed. Here are a few design and development tools that I've come to rely on that don't have the exposure of something like Photoshop.

• Frank DeLoupe from Jumpzero Frank DeLoupe is a great little loupe and color picker app that lives in your menubar and integrates with Photoshop. You can choose to copy colors in pretty much any format you'd want like RGB, Hex or UIColor.
• GitBox from Oleg Andreev GitBox is a GUI front end for the Git version control system. While I still prefer the command line for more advanced operations I like GitBox's simple UI for making basic commits and looking at previous changes. I also use GitBox to help keep track of what's going on in both my work and personal projects as well as other open source projects that I need to keep an eye on.
• Kaleidoscope from Black Pixel While Kaleidoscope has gotten a relatively large amount of press I'm going to include it anyway. The new version is the best diff tool I've ever used and it has become a major part of my daily workflow. It integrates well with GitBox and makes reviewing code changes, and even image asset changes, much easier.
• MockSMTP from Xilinus MockSTMP listens for SMTP connections on your Mac and makes developing and testing web apps that need to talk to an SMTP server much easier. Messages sent to its port number are displayed in a Mail-like interface and you can view them as HTML, plain text or the raw message with headers, mime-parts and all.
• ScreenFloat from Eternal Storms Software Describing ScreenFloat is always a bit of challenge. Yes, it's an app that takes screenshots but that's not really the point. What makes ScreenFloat useful is how it displays these screenshots. Screenshots taken with ScreenFloat are displayed in a small window that floats above all your other apps. A few days ago I needed to update a view that uses Auto Layout and I just took a screenshot of the view's constraints in Interface Builder before I started moving things around. When I was ready to reapply those constraints it was easy to refer to the original set. It's kind of like having a photographic memory.
• Screeny from Drew Wilson Screeny is a quick and easy screen recording app. I mostly use it for grabbing quick videos of interface animations and bugs for sharing with other developers and remote team members. It probably wasn't the best tool for the job but I even recorded the OnePAD screencast with it.
• Slicy (née LayerCake) from MacRabbit Anyone who does web or UI design in Adobe's powerhouse image editor owes it to themselves to check out this app. All you need to do is organize your files into named layer groups (see the examples) and Slicy will export your assets. It can even generate your 1x or 2x versions automatically.
• Soulver from Acqualia Software Soulver is hands-down the best tool I've found for calculating layout dimensions. If you design software with a user interface you should have this app. There's also support for variables and line references and all kinds of other great stuff.

Give them a try

While Frank DeLoupe and Screeny are only available on the Mac App Store, the rest of these apps have a free trial available and you should give them a look if you haven't already.

Updated: I just received a recommendation for ColorSnapper as an alternative simple color picker. While it doesn't integrate with Photoshop, I like the way it lets you pick two different formats without having to access the preferences. (Thanks Brian.)