Without any wildcards (cards designated to represent any card wanted), the Royal Flush is the highest possible hand in straight poker play. Though the origination of poker is disputed, Hoyle is accepted for first publishing the ranking system in poker in 1937 and still used today as the official ranking system for poker hands.

The rankings and odds of getting a particular hand are:

1. Royal Flush 649,739 : 1

2. Straight Flush 72,192 : 1

3. Four of a kind 4,164 : 1

4. Full House 693 : 1

5. Flush 508 : 1

6. Straight 254 : 1

7. Three of a Kind 46.3 : 1

8. Two Pairs 20.0 : 1

9. Pair 1.37 : 1

10. High Card 0.995 : 1

Texas Hold'em has become the most popular poker variation on the professional card playing circuit, with players competing in tournaments for millions of dollars.

More Info: en.wikipedia.org