One of the reasons I originally became interested in Pathfinder, was it's stated compatibility with 3.5.
So in peoples experience, are spells from the splat books compatible "as is" with Pathfinder ?
Pretty much. The only things that Paizo changed as far as spells go are the spells the were overly complicated or game breaking. If it's just a traditional 4-6 sentence spell there's no reason to be too concern it won't work.
Did you have something in mind?
Nothing specific at the moment, I have been working on some different Sorcerer bloodlines, and Oracle foci for our game....and I would like to use spells from the Spell compendium, and some of the other splat books;)
Rather than start a whole new thread on this, there are several threads out there talking about compatability of Spell Compendium.
Here is a quick search.
The short answer is they are no more or less balanced than they were in 3.5.
(Not trying to be snippy by pointing you to a search, but it's really been discussed a good bit).