iStat for iPhone?

I don't know if there's an exact battery time left indication, but since battery time varies by what you're doing and phone settings such as screen brightness (as well as things like ambient temperature), I don't know how accurate or useful that'd be anyway. The battery indicator in the main info bar should give you a good estimate, and it does pop up a warning when it gets to 20% and 10% (or what it thinks those % are anyway).

For memory capacity & remaining info go to Settings > General > About

We don't have any battery stats in iStat yet, but are looking into it.

As WhySoSerious said, battery usage will vary A LOT, depending on what you're doing. Listen to music while surfing the net non-stop or playing a complex game, and you'll cut your battery time down to a fraction of what it could be.

Turn off 3G and only send text messages or use "light" apps, and you won't need to charge for a while.

Still... we are looking into it. We want iStat to do quite a bit eventually.

I just put an app called "Free Memory" that gives all stats like every process running and memory consumption as well as battery level. It also gives you the ability to Free up to 20 MB of runtime memory, I'm not sure if that was what you were asking but there it is.