Runny nose due to allergies:
-fluticasone (flonase) nasal spray = 1st line.
-then loratadine (claritin) or cetirizine (zyrtec) 2nd line--these must be taken daily to see benefit. Could also add fexofenadine (allegra) to this list. Might have to try different ones to see which one works best but they're dirt cheap
Otherwise if not from allergies...
-best decongestant = pseudoephedrine (old sudafed formulation, depending on state / pharmacy, may have to get a prescription for this if they won't sell OTC--ask the pharmacy or check state laws, small independent pharmacy may be willing to if chains are not)
-sudafed NOT behind the counter = sudafed PE = phenylephrine. Doesn't work as well as original sudafed (pseudoephedrine) and will CRANK your BP if susceptible. Personally don't recommend this one.
-best short-term use = oxymetazoline (afrin) nasal spray-- do NOT use more than 3 days in a row or you will experience rebound congestion. Dirt cheap. May raise blood pressure so monitor closely (didn't for me and many others, but it's possible).