It depends on the size of the app and whether or not you will also use your iPod touch for music and videos. Apps range from 1MB to 200MB, so if you are ONLY storing apps, then you will be able to hold around 800 apps.
The iPod Touch 8 gigabyte can hold up to 1,750 songs and 10 hours of video content. The maximum number of apps you can fit on your iPod Touch is 144 depending on the size of the apps. However this number is being increased to over 6,000 with the iPhone OS 4.0 update with the addition of folders.
Finding out the number of apps it will hold depends on how much space it takes up. It also depends on how much media content(music, movies, etc.)is already on it. So, basically, there is no definite answer.