From publisher blurb:
Although a vast number of spells are available in the game's core rulebooks, many GMs and players have an insatiable desire for more options. In many cases it's not necessary to create new spell options from scratch, since a few minor changes to an existing spell can create something with a very different feel or impact on game play. These spell variants are based on the idea that you can make a lot of different effects with fairly minor changes to how a spell works, or by combining effects of multiple spells, or by mixing a spell and magic item or even a class ability (preferably from a class not used in the campaign).
Some spell variants are common and fairly obvious, such as having an iceball spell that is a fireball that deals cold damage. The following list of one hundred ten spell variants are slightly more complex and are designed to show how you can create new spells without too much work. One important tip is that when you base a new spell on an old one, many details—such as its school, components, duration, and often even interaction with other spells—is already determined. Similarly, you can often create spells that have entirely new themes just by changing casting time and legal targets. This last trick is often a great way to make spells appropriate for new classes.