I haven't watched a whole lot of anime, but each one I've watched has had a really good opening to it, especially the music. Some are really catchy, even if I have no idea what's being sung in the JPN language openings.
UBW honestly has some of the best animation I've seen. So good.
watched this as a kid but it's still really memorable for me
And Spirit mentioned it, but Steins;Gate's opening is really good as well.
I'm not really that big on the openings, and also i don't watch super-much anime. However, the original opening for Pokémon is iconic to me and I can't not love it. Also original Yu Gi Oh series is pretty nice! IT'S TIME TO D-D-D-D-D-D-D-D-D-D-DUEL!
Heroes join the operation
From different planets and different nations
There's an intergalactic federation
To monitor the situation
Catch each and every confrontation
Only broadcast on this station