Roxanne's Glue-Baste-It is excellent for placing applique pieces. It just takes teensy little drops, sets up quickly and washes out. Available at most LQSs, Connecting Threads, etc.
Elmer's washable school glue stick is good for paper-piecing. I use it to hold the first piece of fabric in place and also some end pieces (after stitching to foundation paper) to hold them in place while trimming.