Eh, I don't feel like finding videos for them because there are so many. =P But some of my favorites are:
Openings:
Code Geass Opening 1 - Colors (Flow)
Code Geass R2 Opening 1 - O2 (Orange Range)
Code Geass R2 Opening 2 - World End (Flow)
Death Note Opening 1 - The World (Nightmare)
Fate/Stay Night Opening 1 - Disillusion (Tainaka Sachi)
Welcome to the NHK Opening 1 - Puzzle (Round Table feat. Nino)
Welcome to the NHK Opening 2 - Puzzle (Extra Hot Mix) (Round Table feat. Nino)
Samurai Champloo Opening - Battlecry (Nujabes)
Bleach Opening 7 - After Dark (Asian Kung-Fu Generation)
Bleach Opening 8 - Chu-Bura (Kelun)
Clannad After Story Opening - Toki wo Kizamu Uta (Lia)
Endings:
Death Note Ending 2 - Zetsubou Billy (Maximum the Hormone)
Samurai Champloo Ending - Shiki no Uta (Minmi)
Bleach Ending 2 - Arigatou (Home Made Kozoku)
A bunch more I don't feel like listing.