I like the free UltimateStatusBar extension.
Visible only when you're hovering over a link, it shows where things lead, but does other stuff too. Like shortener expansion and favicon previews.
It's got lots of built-in themes you can use to customize the appearance.
iOS does not have an option for this, nor does apple approve apps which alter the status bar. If you want this function you will have to jailbreak your iOS device and install a third party status monitor. As pointed out in another answer, LockInfo does this. SBSettings used to, but no longer does. If you're running an iOS 4.x device, OpenNotifier might be useful as it does this as well as give you pull-down notifications similar to android and iOS 5.
If you're developing for this device, however, you can add this function yourself. As a developer you can run custom code without jailbreaking the device - you just can't submit that code to the app store.
The trick, then, is going to be finding example code for this feature. I expect someone in the jailbreaking community will have some info on what the code needs to do, and if you're lucky you'll find an open source project for it. Then you can compile and sign it yourself, and as long as you keep your ad-hoc license current and recompile/re-sign it yearly, you can use it on your personal devices.
I think a lot of developers overlook the fact that they can run any code they want on their own devices without jailbreaking. They can also distribute such apps in a limited manner to their friends using adhoc distribution as well.
It looks like OpenNotifier is open source, and has the functionality you need:
https://github.com/n00neimp0rtant/OpenNotifier
I don't know much about the status of the project, but it might be usable for you as a developer to bring this functionality to your devices.
Best Answer
So let's go through the options here:
defaults write com.apple.Safari ShowStatusBar -boolean trueWhile searching around though, I found a great deal of people asking how they force the bar to autohide. It's a common complaint in editorials as well, and seems to be the one constant of all the Safari extensions.
After an extensive search - what you're looking for does not exist at this time :(
Hardly the first time Apple has taken away control from a user, either...
Tl;dr: Apologies, but it's time to let it go - it's gone.
HOWEVER....
One of the extensions I found is open source and appears to be easily editable. Specifically, this one, and by removing a line of JS, I can force the bar to stay on the screen, and replace it with blank text (so it looks correctly).
Here's the thing, it's still just an overlay on top of the page, it's not a part of the safari "window" as the old status bar could be, and doesn't show all of the same information either.
Here's what the effect looks like
And here's the extension package. You can see the changes made from the official release to make this possible as well.
Installing this requires jumping through an extra hoop since I'm not a registered Apple dev, so here's what you need to do.
Usual disclaimers apply, your mileage may vary, void where prohibited, kids eat free, etc.