The front door is the centerpiece of your home.  It's also the first thing that a buyer sees and touches when they visit.  That initial impression is important -- and easy to update.  It's definitely worth the money and time to make it attractive.

Get some good house numbers -- local Home Depot or Lowe's has a large variety in stock.  Remember to consider the style of your home when you select doors.  A stately traditional Georgian home looks odd with Modern numbers, a Craftsman style home should not have mid-century font. 

Update your hardware. (Make sure it all matches: numbers, hinges, hardware) My favorite is Rocky Mountain Hardware, which can be ordered online. 

Paint or stain your front door.  This site makes it very easy: The Dutch Door Kit from  Vermont–based Fine Paints of Europe includes all the necessities for transforming a front door: sandpaper, primer, solvent, brush, and paint—one Euroquart of brilliant or satin Hollandlac enamel in any of 32 colors on the Classic European Color Chart; $100 (a $128 value).  Don't forget to paint the threshold!
Remember to take a good look at your door before you go to the trouble of new paint or hardware -- does it need total replacement?  Ask an honest friend.  If it's an 80s style leaded glass door, update it.  Luckily being in Houston we are close to a great discount door center: http://www.doorclearancecenter.com/.  

Paint Type: There are two schools of thought in Houston -- One says using oil paint is the way to go, and the other says using latex is better.  Either way, we live in a humid city and mold spores will develop after a year or so.  I don't think there is anything that will give a door a glossy look like true oil paint.