I second Shockwave Pulsar, It was a great Blue Magic, much better than anything Kimahri had to offer.

I'd like Shadow Flare and Pandora's Box (both FFVII) to appear again, but only if they were accessible nearer the beginning of the game so you could get some use out of them.

W Wind (FFVI) would be nice to see again. 90% damage to anything.

Strago's Grand Train should make a comeback, as should Quick (already mentioned by Slade).