Thought I'd resurrect this since Orange and Vodafone are now doing the iPhone so no doubt lots more folk looking for suggestions (myself included). The app store isn't half full of rubbish unless you know what you're looking for.
So far I've downloaded, and liked, the usual (free) suspects, ie. facebook, skype, flickr and echofon (for twittering). Also liking WifiTrak for searching for wifi spots.
Camerabag is nice for only £1.20. I've never been a huge fan of cameras on phones and as such never used mine much in the past, and the iPhone camera is probably one of the worst on the market, but the effects and filters available with Camerabag are impressing me, turning dull snapshots into stuff worth uploading directly to flickr etc without having to muck about in photoshop. I'm already finding I'm using the camera more because of that.
Also got one called Think Ink, which as a designer is going to come in handy. Can take a sample from a photo or any chosen colour and come up with a range of colour combinations that fit, with an RGB and CMYK breakdown of each. Might be quite handy if you're looking to redecorate, take a picture of your new couch and choose some paint for the walls
. There are more comprehensive versions of the same thing out there, but so far it's the best free one I've seen.
But the best app I've got so far, is the most expensive. £12! I never thought I'd spend that much on a phone application, but damn it's good. If you're into creating music at all, (particularly electronic/dance or variations thereof) then you really
must download
Beatmaker, even for just mucking about it's worth it. For me, when coupled with the free desktop application that allows you to create your own samples/loops (though it comes with some fantastic ones already), it shows what the iPhone is capable of, ie bridging the gap between computer and phone. It's the kind of software that 5-10 years ago would have cost you £1000+ plus the cost of the computer and midi equipment to run it. But it's only 12 quid and you can carry it in your pocket! Just awesome.