Actually, it looks like Smultron development just started back up - conveniently (and I'm sure coincidentally) just in time for the App Store to launch.
If you're looking for a still-free alternative, I've only briefly used it, but everyone says Fraise is a good successor.
I would recommend Smultron as a text editor for mac*. X-code, though personally I never used it, is probably just a huge confusing mess, a plain text editor is a much better start.
* unfortunately, it seems Smultron became a pay-for app sometimes since I last looked, but I guess you can find the old versions somewhere on the internet, which were free.
I used to use a tool called Taco HTML Edit. It was free years ago and was pretty nice. It's now $24.99 (cheap!) and has a lot of features comparable to Panic Coda, which is $99. It's come a long way and is another solid text editor to add to the list for OS X.
There's also Smultron with its famous strawberry icon. I haven't used it in years but it was a decent text editor if I recall.
I've tried Flow because I had gotten it during a MacHeist, but it's a commercial application at $30 and apparently only supports FTP right now.
Edit: As for syntax highlighting text editors, I used to use Smultron, which was also free, but apparently after the introduction of the App Store and Lion it has now become commercial.