In 1992 Dale Grote of the University of North Carolina, Charlotte, web-published what has become a classic in its own right — a very detailed, chapter-by-chapter study guide for Wheelock's textbook. The Guide offers alternative explanations for the first 35 chapters, and helps get to the heart of Wheelock's discussions.
Written by Paul Barrette of McMaster University, Canada, this site boasts a full range of vocabulary-oriented drills for Wheelock — although it is currently keyed to the previous edition (which is not radically different from the current one). The user interface is easy to use, and the drills run quickly.
Elizabeth Sutherland from the University of Tennessee, Knoxville, has provided two sets of Latin drills: one for verbs, the other for nouns. The drills test one's knowledge of paradigms — that is, vocabulary words that illustrate common patterns in the language.
Yes, there are more complete and more thorough Latin dictionaries on the web, but for simplicity's sake this one is the best. The dictionary was written by Tze-wan Kwan and Chong-fuk Lau at the Chinese University of Hong Kong, based on a word list by Lynn H. Nelson of the University of Kansas.