I've always liked giant spiders as denizens of fantasy worlds, ever since my young mind was introduced to them by way of The Hobbit. Spiders are creepy to begin with in the real world, so it seems only natural to imagine bigger and deadlier versions lurking in the dark places between the points of light in D&D. Imagine my surprise when 4th edition only offered up a couple of variants of this classic monstrous vermin, and none that were simply a low-level Giant Spider (as vanilla as that may be). (Update: the Monster Manual 3 offers up the Ambush Spider, a 2nd level lurker).
Desiring an creepy but simple-to-run arachnid for my game, I quickly threw together a Giant Spider of my own, using the Deathjump Spider (MM) and Bristle Spider (MM2) as templates.
To add to the creepy-crawliness of the encounter, I also whipped up some Spiderlings, minion versions of the Giant Spider. They lack the poisonous sting of their mother, but possess that uncanny spider talent to move out of the way just as you're swinging a
Add in a few squares of spiderweb terrain (DMG p.69) and a couple of Giant Spiderweb Traps, and you have an encounter fit for beginning adventurers. (The newly released Monster Manual 3 contains a sidebar [MM3 p.183] presenting cobwebs in which spiders can hide and web sheets which are similar, but less potent, than my homebrew Giant Spiderweb Trap.)