Plumbing parts are Legos for adults. There are so many different shapes, sizes, & pieces that you can use to make legs for any type of table. The key is to add support bars or increase the width of the pipe you use as the weight of your table-top increases for stability. Plumbing parts aren't the cheapest legs out there, but they're certainly not the most expensive & they look really cool!
First, here are the basics...
Step by Step
Gather old wood & cut all of the pieces (except one--set one aside) to the same length (any length that you'd like your table top to be). Then, cut the piece you set aside into two pieces that are 1-2" less than the width of your table. These will be the support braces that hold the planks together.
If you can't find old wood, try the bargain bin at the hardware store & use these tips to artificially age it in an afternoon.
Lay your table top plank pieces face down & place the two support braces across the pieces. Put at least one screw (a few more--one in each corner & then a few down the middle is better) into each plank (make sure your screws aren't too long so they don't poke through your table top). Screw plumbing flanges into the table top to attach your plumbing pipe legs.
Screw your pipe legs into the flanges & add finishing touches. use a sticker scraping razor to remove price tags & add plastic feet to keep the table from scratching your floors.
You can also flip the table over & seal it with wax or polyurethane.