OP, what kind of apps do you want? Beer-related or general purpose ones? I have an iphone not an ipod touch, but most of these apps should work the same.
Gizmodo lists some "essential" apps, and is generally pretty reliable. They also do weekly reviews. Here is a link to their most recent guide: http://gizmodo.com/5676549/gizmodos-essential-iphone-apps-october-2010
For beer-related ones, I use BeerAlchemy on the iphone. I don't have the Mac version; I do it all here. I used to use ProMash, but I was tired of it not being maintained. It's a little pricey, but I found that it is very usable. I also have Brew Pal that I use only to do recipe conversions for Zymurgy. It doesn't have many features, but it's not bad for one-off calculations. It's quick. BJCPstyles is the other one I use regularly. I also use Calculator and Convertbot for math and for unit conversions.
Non-beer related ones that I use regularly:
Twitter bought the best paid client out there, and now it's free. That's a good client. I use BeeJiveIM for instant messaging. The free Google client is quite useful, not just for voice searches but also for email.
The free Alarm Clock app is pretty useful, particularly after multi-tasking was added to the OS.
If you travel, I like FlightTrack. It costs some money, but I use it every trip.
The Weather Channel app is a good free weather app with more info than the built-in app.
Games are a very personal thing. Depends on what you like. I use iBridge Baron all the time, and Enjoy Sudoku as well.
Pandora is good for music. Shazam is very cool to answer the "what's that song"? question. I use IMDB for the same purpose on movies.
If you use Netflix, their app is great for on-demand viewing. Works very well. I use i.TV for looking up TV listings, and Fandango for movie times.
CheckPlease Lite is a great free tip calculator. ESPN Score Center is cool for looking up sports scores.
Those are ones I use regularly. I have a lot more apps on the phone that I use rarely. I also left off a lot of the location-based ones since you need to have a network connection to get value out of them.