Pretty much anything they could get their hands on. Scandinavia may have not had good metal resources, but they had an abundance of good ash and oak wood to make spears out of.
For the most part, they'd be about as long as you mentioned (8' or so) depending on how they were using it. Most only fought with their spears for a short while before throwing it, while some just threw their spears before the lines met.
Most Germanic/Scandinavian armies had only two principle formations: the Shield Wall, and the Boar's Snout.
The shield wall was about how you would imagine; the men would all stand in a line with their shields locked together, forming a "wall." Given that the shield sizes were not uniformed, the formation wasn't as precise as anything the Mediterranean countries used in combat. In a shield wall, shorter weapons were preferred to allow plenty of mobility for getting around the opposing forces shields. Thus, most spears didn't stay in the hands of men much after the initial skirmish.
The Boar's Snout, on the other hand, was pretty much an "anti-formation." It was the medieval equivalent to the modern wedge formation. Essentially, the strongest warrior would lead the charge (in Beowulf's case, he would be that man) followed by the next strongest behind him. The idea was to pierce the the shield wall in the same way an ax pierces through wood. In these conflicts, missile weapons were lobbed before the actual hand to hand combat took place. This would usually by thrown axes or spears.
^Hm, so they kinda pretty much combined tactics that both Rome(wedge and spear throw) and Greece(phalanx aka 'shield wall') had before them. Interesting.