When i'm down I listen Driver's high from GTO and it energized me!

yup...
i'll waiting for you from Bubblegum crisis tokyo 2040

Dark chi theme, Let me be with you, babble of love. all from chobits really LOL but they did the job very well

Tank! from Cowboy Bebop. Love the opening horns.

Tsubasa wa pleasure line from chrno crusade 'Op.
and Sayomara Solitiare from chrno crusade Ending

for me is "heart of the sword" ending of rurouni kenshin the tv series a very strong song

well, yeah. "Moon on the Water" from Beck and "Dream Believer" from Prince of Tennis. I really love them! =)

A song that lifts me up? I don't know! I usually go for the melancholic songs in Anime.. i love to cry while hearing "Watashi tachi ni naritakute" -Sailor Moon- or Thanatos (If i can't be yours) from Evangelion...
But for cheering me up i'd probably chose "Let me be with u" from Chobits, "Love Panic"-Ranma 1/2, "Tobira wo Akete" from CCS (that's a major energizer!).. Anyway, there r really cute songs out there!

Megumi Hayashibara - Risky Gamble. I believe its from the Slayers radio story. I love the energy and bassline in that song and Megumi always makes me happy.

mhmm a pick me up song.. well it's not so hyper but i like how it comes together and makes me smile.. the ending theme of Honey And Clover - Waltz <3

Songs that can pick me up...
Catch you catch me; Tobira wo Akete; Fruits Candy (Card Captor Sakura)
Omoi wo Kanadete (Uta~Kata)
Ichigo Complete (Ichigo Mashimaro)
Innocent Starter (Mahou Shoujo Lyrical Nanoha)
Scramble! (School Rumble)...
And many more ^^

Come from inuyasha
harmonia from naruto
crybaby from otogizoushi
mr de javu from getbackers

and many more !

Mahoro de Mambo from Mahoromatic always makes me happy!...Gotta dance now! ^^

Normally "haruka..." from Kamikaze Kaitou Jeanne will cheer me up.

well, the song that I hear when I try to be more happy is Zankoku na tenshi no tezze...that song always make feel very good!

cowboy bebop's Tank!
and my beloved one, tenjou tenge's opening Bomb a Head

Konnya wa Hurricane from BGC
Good Luck from Appleseed
and curiously the fight song from Macross Plus (the desert duel between Isamu and Guld)

hMm...WeLL i wiLL lIsTEn tO RiVeR..OR fiElDS Of HoPe...Or AnY Gs AnD GsD SoNG...i lOvE ThEm sOo mUcH....i Also lOvE dA tSuBasa sOnGs...ThEy'rE GreAT!

hahaha, ZeroFear, I understand you!

Those Pokémon songs really pick me up too. xD~
It happend to me many times when listening to "Do Ya Really Wanna Play"... I just start dancing without realising it. Weirdo me.
The "Johto League Champions" is another classical. It makes me excessively happy suddenly.
PKMN rules ^^

This songs:
Honoo no Tobira (G.S.D)
Arashi no de Karagayaite (G 08MSTM)
Information High

Let's see.... the opening and closing themes for Fruits Basket always make me feel a bit better. Anything Fruits Basket makes me feel better, though. ^-^!
I love the show/manga in it's entirety and when ever I put it on it first cheers me up, sends me into a horrible wave of depression for the character who is suffering today, and then it cheers me right back up with Tohru's genki attitude. ♥

There a few I think

Every Heart - BOA or Inuyasha
DTechnoLife - Bleach
ending of Chrno Crusade

One Piece ending ~Fish~ quite a great song Y'know...

Disillusion Fate/Stay Night :3!