I'm about to expand my collection of Wii games and DS and I needed a help from forum members to have a better perception that buy games. So I opened this topic. You can post your best/favorite games for the Wii and then your best/favorite games for the DS. 

DS Games
10.Pokemon Pearl/Diamond
9.Kirby Mass Attack
8. Mario and Luigi: Bowsers Inside Story
7. Pokemon SoulSilver/Heartgold
6.Mario and Luigi: Partners in Time
5.Kirby Squeak Squad
4.Mario Kart DS
3.Legend of Zelda Spirit Tracks
2.Pokemon Black/White
1.New Super Mario Bros

Castlevania Dawn of Sorrow
Castlevania Portrait of Ruin
Advance Wars Dual Strike
Advance Wars Days of Ruin
Retro Game Challenge
Feel the Magic XY/XX
Final Fantasy 4
Contact
Resident Evil Deadly Silence
Chrono Trigger

Wii Games
10.Rayman Origins
9.Super Paper Mario
8.Sonic Colors
7.Super Mario Galaxy 2
6.Legend of Zelda: Twilight Princess
5.Donkey Kong Country Returns
4.New Super Mario Bros Wii
3.Kirby's Return to Dreamland
2.Legend of Zelda: Skyward Sword
1.Super Mario Galaxy

Xenoblade
Metroid Prime
Twilight Princess
Mario Galaxy
SSBB
No More Heros
Kirby, Return to dreamland

The World Ends with you
Ghost Trick
New super mario bros

Mario and Luigi, browsers inside story

Pokemon black/white

Will update later

I honestly haven't played a ton of DS games; all I could really suggest from there are the Ace Attorney titles.

As for Wii:
Metroid Prime 3 (or Trilogy if you can find it)
Donkey Kong Country Returns
Super Smash Bros Brawl
Okami
SMG if you enjoy platformers

Can't recommend either of the Zeldas for the Wii; Skyward Sword is super tedious with a huge tendency towards hand holding and lots of fetch quests, whereas Twilight Princess is mostly devoid of original ideas and what is new (such as the Wolf mechanic) is poorly implemented.

My top ten wii games: 

Skyward Sword

Twilight Princess

Super smash bros brawl

Mario Kart

Xenoblade

Call of duty black ops

Animal Crossing

Mario Galaxy 

Mario Galaxy 2

Goldeneye 007

Metroid Prime 3

Favorite DS games 

Pokemon Black 2/White 2

Pokemon Platinum 

Pokemon Soulsiver/heartgold

Pokemon Black/White

Pokemon Diamond/Pearl

Zelda: Phantom Hourglass

Pokémon Mystery Dungeon: Explorers of Time / Darkness

Mario Party DS

Super Mario 64

Mario Kart DS

1) Super Mario 64 DS

2) Super Mario Galaxy 2
3) Super Mario Galaxy
4) Pokémon 4 gen
5) Super Smash Bros
6) Mario and Luigi Bowser inside Story
7) Xenoblade
8) The Last Story
9) Mario and Luigi Partner in time
10) Pandora Tower's

Yep... i don't like Super Mario.

That has already sort of been done:

GamrConnect Wii Recommendation Thread

GamrConnect DS Recommendation Thread

DS:
EBA, the 2 zeldas, pokemon hgss and bw2, chrono trigger DS, diddy Kong racing, MK and nsmb are cool too.