You sound like my grandson.... XBL is really cheap for him, his parents pay for it.
(no offense)

Technically my parents don't pay for anything besides gifts, but without a job the money comes from somewhere.
I 100% recommend the first two. I put them at the top for a reason. Qubed is actually 3 XBLA games.
Metacritic Scores for
* Qubed (XX)
* Every Extend Extra Extreme (78)
* Lumines Live! (77)
* Rez HD (89)
LUMINES LIVE! - Standard Edition (12 skins). Additional Premium Downloadable Content Included: Advance Challenge Pack, Rockin' Holiday Pack, VS CPU Pack, Puzzle/Mission Pack Puzzle, Tokyo Club Mix Pack, Heavenly Star Skin, Breeze Skin.
According to the DLC listing on the Microsoft website, the only DLC not included is "Booster Pack". ($7.50/600)
The individual games would cost $30/2400 space bucks, not counting the deals of the week. If you were to purchase all of the content in this pack, (before Nov. 14, when two skins stop being free) it would cost $78.75/6300 space bucks. If you decide to buy the booster pack that Atari decided they wouldn't include*, you would still only pay $27.49 with this pack.
*Bastards, there's more than enough room! They could include every theme and gamerpicture for all three games and still be like 6 GB short of filling the disc! Still a great deal.
Namco Museum has 9 XBLA games, with 200 achievement points each:
Galaga Legions,
Pac-Man Championship Edition, Mr Driller Online, Pac-Man, Galaga, Xevious, New Ralley X, Dig Dug and Ms Pac-Man.
And the following hastily ported games: No leaderboards or achievements, more like how they were originally.
Baraduke, Bosconian, Dig Dug II, Dig Dug Arrangement, Dragon Buster, Dragon Spirt, Galaga '88, Galaga Arrangement, Galaxian, Grobda, King & Ballon, Mappy, Metro-Cross, Motos, Pac & Pal, Pac-Man Arrangement, Pac-Mania, Pole Position, Pole Position II, Rally X, Rolling Thunder, Sky Kid, Sky Kid Deluxe, Super Pac-Man, and The Tower of Druaga.
Along the same lines are two games I haven't played. Sonic's Ultimate Genesis Collection and XBLA Unplugged.
Sonic's Ultimate Genesis Collection:
Read the list at amazon, it's a little big. There's a lot there, but the developers purposefully made it so you can't play Knuckles in Sonic 2, Sonic 1 and Knuckles (blue sphere), or S3&K. In an unrelated event,

a few months after they made this they released the XBLA game Sonic and Knuckles! Now you can lock on with your already purchased wastes of money Sonic 1, 2, and 3!
XBLA unplugged:
5 XBLA games, all with achivements. Geo Wars is a shmup too.
1 month of live (retail $8)
Bejeweled 2 (retail $10)
Geometry Wars: Retro Evolved (retail $5)
Hardwood Backgammon (retail $5)
Outpost Kaloki X (retail $10)
Wik and the Fable of Souls (retail $10)
Texas Hold 'em (retail $10)
So many edits, so little time. Sign up for XBL silver. It's free, and that way you can track your achivements and when they were earned.