What applications should I delete?

Run monolingual to rid yourself of unnecessary language packs. Remove iWeb/iMove etc if you don't think you'll use it.
Other than that the rest aren't really huge hard drive hogs.

 

You have to be careful with monolingual because you can accidentally remove some files that will leave your MBA with a useless keyboard.

 

Based on my experiences, I would delete iTunes, iWeb, iPhoto, iCal, iMovie, GarageBand, and iDVD. Your usage on any of those programs might differ.

 

Xslimmer is more reliable, as it has a black list of applications not to be modified (some experience problems later on).

 

Just deleting applications will not gain you that much room.

I would follow the steps in this guide.

http://guides.macrumors.com/Complete_Steps_to_Perform_a_Clean_OS_X_Reinstall_on_Your_MacBook_Air

I am also a fan of x-slimmer.

Hope this helps.

 

Deleting garage band may help a little, deleting all the loops that come with garage band will help a lot!
Also iWeb and iDVD themes can be quite large IIRC
Look in /Library/Application Support/Garageband - 2.5Gb on my system
I also upgraded from leopard, thought that snow leopard would remove all unnecessary printer drivers, still, just found a gigs worth in /Library/Printers