University of Texas at Austin
Ser and Estar One More Explanation
This site explains the tricky grammatical option of the two "to be" verbs, ser and estar. The following situations are discussed: joining two nouns, adjective phrases, and prepositional phrases.
Other
Bowdoin Coll.: Spanish Grammar: Verbs Followed by Prepositions Before Infinitive
Many verbs need a preposition before an infinitive. This site provides a substantial list of verbs which require a pronoun before an infinitive and the meaning of the phrase it creates.