Ok I installed Electrum portable on a USB stick, I have a balance on an address that i made offline with the bitaddress.org webpage and has never been imported anywhere.
Now I want to import the public key for that address as a watch-only but I can't figure out how to do it. I can only see options to import files and private keys.
Hm, Maybe I should post this in technical support.
You don't need to use both Electrum and Bitaddress in conjunction. When you first ran Electrum it will randomly generate a 12 word seed that will be used to generate all the future addresses of your wallet (hence it is a deterministic wallet) - password protect this wallet. Then from there look at the tabs at the top and find the one stating 'Master Public Key'. Copy the text string onto notepad and bring that to your main online computer. From here begin your fresh installation and select "Create a watching-only version of existing wallet", you will then be prompted to enter your "Master Public Key".
The trade off with Electrum (at the moment at least) is that you cannot 'watch' imported addresses only ones created via your original seed. Nonetheless, unless your creating vanity addresses it shouldn't matter - an offline Electrum client will create keys just as safe as bitaddress.
Refer to here for more info:
https://electrum.org/tutorials.html