(The picture was taken from: http://www.technicaltradingindicators.com/tradestation-indicators/83-candlestick-patterns/)
Depending on the time frame, a candle like Hammer or Shooting Star can be a clear reversal signal as it shows enormous buying/selling pressure on the coin. It does not require trendlines or other indicators to be able to project future moves, especially if the candle was formed on a daily time frame or higher.
Another very important single candle you will need is the one that appears during a blow-off top or capitulation. Those two are the reversal points in a trend, where the price makes an explosive move which then very quickly retraces. It is an indicator of a buying/selling climax that is followed by other people leaving or entering the market in an accelerated movement. A candle like this usually is massive and has a long wick which is later followed by another few candles that represent this accelerated buying/selling.
Candles can also create a specific pattern within a group of 2 or more, that also works as a great reversal or continuation signal. From the most popular ones, we would distinguish tweezer top/bottom and either Evening Doji Star or Morningstar. Those are reversal patterns that we personally often use to confirm our entries or exits.