CROSSTAB and FOR XML PATH would be the most popular around here, there are loads of examples on ssc. FWIW there's a similar thread here.
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden