So what to cover it with? well lets start with good old fashioned felt
1) Standard green felt

The problem though is that it will only last a couple of months before it start pilling up. Soon your table will be covered with hundreds of little tiny green felt balls of fluff that ruins the whole look and feel of the table.
With standard poker table felt the cards also wont slide as well as you might expect. standard felt really isn't the way to go unless your table is going to get minimal use. you should be paying around $30-$40 to cover your table with this
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2) High quality felt (like the stuff they use on pool tables)

3) Velveteen
Velveteen is my personal choice and the choice of a lot of home poker table makers. Don't get it mixed up with crushed velvet( its rubbish to use on poker tables, the cards wont slide well at all) or standard velvet(the pile is too high and it will feel like your digging around in one of grandmas old sweaters)
This is how my table came out, unfortunately the camera doesn't capture just how nice velveteen looks.

*Velveteen feel really nice to play on, its very soft and has a mild "furry" feeling to it.
*It looks incredible! it has a kind of shimmer to it and many different tones (the sort of thing you would see in the morning when there is dew on the grass)
*Card slide across it very easily, it really looks like they are floating on a layer of air. But don't worry its not too slippery. your chips and anything else on the table will grip nicely, it only affects the cards.
*Its durable, it will last for ages, but keep cigarettes away as it will melt a hole in an instance and will mark if you leave heavy objects on the table (even a glass overnight left a small ring in mine which is slowly "uncrushing" itself the more it gets used.
*Velveteen is nice and cheap also. to cover your table you will be paying around $30 to cover it. i got mine as cheap as $24.
So from my experience Velveteen is the nicest easiest way to go, its cheap, will last longer than standard felt and will look and perform better than expensive felt. Its easy to come by as well, most fabric stores should stock plenty.
Well that's it, get out there and start covering your poker table with a nice playing surface, or alternatively scrub up your skills and play some poker