My 4.65" Galaxy Nexus fits fine in my pocket, and can be used one handed. I've seen an S3, and at 4.8" it isn't as bigger as you might think just by going by screen sizes. Note that these phones are still thin (in the sense of width), and the extra size comes from height (e.g., the 4.8" S3 is only 4mm wider than the 4.3" S2), so the on-screen keyboard in portrait mode isn't going to be that much bigger, so still fine for one-handed typing.
Can I ask if you've used these devices? If yes, fair enough, but if not, I'd recommend you give them a try. The fact that phones are very thin means they are less noticeable in a pocket. (And even if you think you don't need one, you may quickly find yourself getting used to the big screen - now my much loved previous Nokia 5800 looks like a tiny feature phone, as does any Apple phone.)
If you want a smaller Android device, then there's the Samsung S2 at 4.3" (not as high end as the latest S3, but still damn good high end specs). There's also the Sony Xperia S at 4.3". And the Droid Bionic that
[color=#284b72]ApochPiQ mentions is also 4.3".
The best Android phones are, in my opinion, mini-tablets
Well as an aside, all smartphones are mini-tablets - there seems to be a recent confusion of using "tablet" to mean something big, but historically a tablet has simply been a handheld/mobile device that wasn't categorised as a phone; small tablets have simply become rarer in recent years, because manufacturers realised that you might as well make any small tablet also into a phone. If we decide it's simpler to still count phones as tablets, then that goes for small as well as big.
