Smultron is an open-source text editor written in Cocoa for Mac OS X Panther with many of the features that you might need. It features easy selection of the opened documents, line numbers, support for syntax colouring for many different languages, support for text encodings, code snippets, a toolbar, a status bar, HTML preview, multi-document find and replace with regular expressions, possibility to show invisible characters, authenticated saves, command-line utility, .Mac synchronisation of preferences and many more features.
I’m trying this out right now and it seems pretty nice so far. (possibly the new free, open source BBEdit hotness?) We shall see.