Wine Notes is the best dedicated journal/tasting notes app that I've seen so far.
That said, I'm migrating my recipe database to Evernote and considering doing the same for my wine tasting notes. Evernote is free, synchronizes with desktop and web-based versions, and features XML export/"backup".
Additionally, I have Cor.kz and find it useful even without a CellarTracker account. I often use it to read reviews when shopping in stores where the selection may be hit or miss (e.g. Grocery Outlet). The barcode scanning works maybe about 50% of the time for me.
I'm sure this is not really what you're looking for but the Liberty School Wine DJ can be a lot of fun. You choose the wine (of course the app is only for LS wines but I use the varietals), mood and setting and the app uses Grooveshark to generate a playlist. Again it's a total novelty and not much use for shopping or cataloguing but I really enjoy it :)
cor.kz is essentially an iPhone interface for www.cellartracker.com
While the app is very useful if you have a cellartracker account (and even useful if you don't), there are still some limitations to the iphone implementation. One of my biggest gripes is that I can't confirm pending deliveries as delivered using the cor.kz app. They also have a barcode scanner built in, but as Kaysyrahsyrah mentioned it's not all that useful unless you barcode tag your own collection which many people do.
They do have a forum on their website (http://cor.kz/) and promise updates and fixes are incoming as well as an iPad version. Apparently they just released an Andriod version as well.
So basically if you use CT I recommend checking it out it even if it's not fully up to speed yet...
Like, yes. Love, no. I'm a stickler when it comes to software apps in general. I want them to solve a problem, not half of one.
Nirvino does a good job with Wine Ratings to help folks look something up, get ratings and info on common wine in stores.
Do not use Red Laser Bar Code Scanner. Wine is notoriously unscannable. Most of my scans come up blank.
Also, no wine app that I know of is worth trying to keep an inventory on. No computer app either.