GoLocker, WidgetLocker, programs like that.
+1 for Go Locker. FREE and so many themes available. It works great.
Just an FYI, you have to be running Go Launcher EX in order to use Go Locker. Widget Locker is a standalone app, but you have to pay for it. Both are very good, but Widget Locker is far more customizable.
Once the official ICS update is pushed out, you will see a new Touchwiz lockscreen, which is actually pretty decent and much better than the current one, as well as other lockscreen options including face recognition unlock which works really well.
As long as you have Go Launcher running when you download and install Go locker, it will still work if you switch back to another launcher. Just don't uninstall Go Launcher. I am using the Go Locker and currently am using TSF Shell with no problems. I purchased and used Widget Locker too, but I really like some of the new themes that are out for Go Locker.