Watermelon Express has GRE Connect (iTunes Link) in the iTunes App Store for FREE (regualrly $24.99) for a very limited time.

The GRE Connect features tons and tons of content; over 1,000+ questions (fully explained), 5 diagnostic tests with detailed statistics, 500+ pages of review material, 4000 words in flashcard format. It also offers real-time feedback and performance analysis for overall performance (score and time), category level progress report, and percentile scores comparing your score with other app users. All app data can be synced with their desktop app which is 70% off for a limited time.