The longboard recommendation is the way to go. There are many companies from which to buy "completes" from, or you can buy each part separately from countless companies to create your own model.
Buying parts separately...
Choose a board that fits your riding style and your size. Go with at least a 38" board. If it's just to cruise around, pick a cruiser or pintail. Some pintails come with a kicktail if you're interested in that potential. Many boards are made with bamboo these days, and it's got a nice resilience and response.
Wheels: If you intend to use it as transportation on the street and uneven terrain, be sure to go with a wheel durometer that is lower (softer). It'll take small bumps and stones much better than a hard wheel. Also pick a wheel with a center-set core (Abec11 makes soft durometer AND center-set wheels).
Choose a wide truck, but you'll have to get used to not hitting the wheels with your foot as you push-kick. lol A lot of guys choose the reverse kingpin truck, but I prefer the old standards.
Don't forget wheel bearings, and risers (so your wheels don't cut into the board in hard turns).
To buy a complete longboard, try companies like Sector9 and Quest... or just go onto warehouseskateboards.com.