Chatology finds the chat logs stored on your Mac at launch and displays each conversation according to the person on the other end. Click any name in the leftmost column to see your full history with that person in the center column, sorted by date. You'll also see the conversation's start time and duration.
You can refine your history by viewing logs from today, within the last seven days, the last 30 or within the last year. Once you've selected a particular history to scour, you can view the full conversation, just images or just links. While testing this app, I was able to find two images I remembered seeing in chat but failed to drag out. It was crazy easy to find them: I just pulled up the conversation, clicked "images" and there it was.
There's a search box, too. Simply type in the term you're after and there it is.
Here's what I love about Chatology. There's a preference to enable Messages integration. When enabled, you'll be brought right to Chatology when you hit Command-F in Messages. It's like launching über-search mode.
Finally, you can export any conversation as a plain text file, use Quick Look to view images and delete a chat log, all from the app.
Those who have lots of conversations in chat, especially those that might include desirable reference information, will do well to install Chatology. Likewise, it's a good choice for users who are not satisfied with the search feature in Messages.
Chatology for Mac is available now for US$19.99 from the Flexibits Store. It requires Mac OS X 10.7.5 or later. Please note that Chatology for Mac will only be available from the Flexibits Store. It will not available from the Mac App Store. Unfortunately, Apple's policies won't allow an app like Chatology on the Mac App Store.
Pick it up now and get searching.