Have you tried the sweet tamarind from Thailand?
They are the best!! They taste sweet, salty, sour, and spicy.
A friend of mine went to Phuket about 2 weeks ago and this is the only thing I asked from her, to buy me a packet of tamarind sweets. She was generous enough to buy me 2 packets and 1 jar.
Now instead of drinking coffee when I feel sleepy atwork, I eat these instead. The sour taste surely wakes me up.