Def get Free App a Day or FAAD I get alot of games through this most of these below I got Free, during the year I pay for some aswell so I don't always know how much they are/where.
This is a very long list but I still play most of these games. And have many more
ALSO TO NOTE NOT ALL GAMES PLAY ON ALL IPODS for 3gs you need 32 Gb and above for infinity blade as you ned multi tasking
Must Buy (IMO)
Infinity Blade (think Punch out for the ipod in HD)
Angry Birds
Hook Champ or its Sequel Super Quick Hook, (not the latest 59p one its ok but not as good as the first two)
Plants vs Zombies
Backbreaker FREE get this
RjDj – free put on headphones with Mic and listen to some funky sounds, these also make the Inception App
Dismount – push a dummy down the stairs, simple but great fun, place a face on the dummy
Train Yard – Free version available but only 59p get this
Very Good Games
Solipskier – draw the ski ramp also you can try this online
Galcon Labs
Gears
MiniGore
MiniSquadron
peggle
Trundle (free but with inapp level purchases not bought them though)
Cartoon Wars 2, a mixture of the original Cartoon wars and Cartoon Gunner -( both of which are good games )
Fastar – simple RPG figh blocks the blocks get bigger
Osmos – aport of the pc version
Spider – the secretes of Bruce manor?(or something like that)
Mega Worm – awesome 8 bit version of that other one with better graphics, think Tremors
Soosiz – this can actually make you feel sick, very nice platformer where the whole world rotates with you/
Zombie Higway – Drive and shoot zombies or run them into cars
Papa Sangre – £3-4 use headphones totaly new experience and wont play on older devices (seems to work on my 32g second gen touch) You have a 3d sound experience really worth it if your device can support it.
Good Games
Cut the Rope
Spirit – use your finger to avoid think simple geomtry wars without shooting, you create loops to capture enemies
The Creeps
Tilt to Live
Veg Samurai (better then Ninja Fruit or whatever its called)
Orbital
Pinball HD
Slay (weird land strategy game) from old PC game takes bit of getting used to but good)
Jet Car Stunts – Think trackmania on the iPod
Maestro – music'y game bird runs on phone line you strum on time to play note
Pix'n Rush very nice game this hard platformer with retro feel that gets mroe retro as you get a higher multiplyer
iStunt – snowborder bit like line rider
Mirrors Edge (for 59p get it)
Monsters ate my homework – throw a ball at the monsters think fairground tin can alley
Nice Games
Perfect Cell – stealthy type game bit like that one game out for xbox last year that I never got, but you follow some girl into a underground base and she gets taken. You can kill but you get points for not doing so.
Slice It
Thumb Wars Free
Ragdoll 2
Super KO Boxing – (think Punch out for the ipod)
F.A.S.T
Gloop - Free I think not a game but very nice physics hard to describe but try it
Sound Juggler
Battle Bears
Antrim Escape – Ecaspe the room type game
Eden – Basic Minecraft for iPod
Ocarina – yes thats right an ocarina for you iPod
Baby Scratch
Melodica
Zen Bound – wrap an object in string sounds dull and it sort of is but really calming and nice change. no time limits.
Crayon Physics – ok on the ipod but not great im told the other draw your own phsyics are better games
Doodle Bomb
Eliss – also weird but worth a try
Auditorium – music bending game weird sounding but nice game
Hysteria – Video based gameplay on quicktime events think those choose your own adventure books in an app
Pour Free – Pour the perfect Pint FREE
Surgeon Xmas – Free
RPGS
UnderCroft – Free from those responsible for Runescape
Zenonia 1 or 2
Pocket Legends (Free MMO)
Track and Field – Yes thats right, track and field with local multiplayer used to love this on my phone but on the iPod I play other games more
Final Fantasy
Jumper/Falling/Running Tpye Games
NinJump Dx
Canabalt
Doodle Jump
Superfall
icedin – very hard as it gets further in but good puzzle
unicorn Attack game
Winterbells
Ultradeep
Puppet Jump – my fav customisation a plenty and a bit silly like the music, but short lifespan
Birdstrike
Hmm OK
Super 7
Polyhedra
Runway – Free version of the other flight control
iQuarium (gets boring quick but nice graphics and very simple look after a fish)
GalagaRemix
Paperboy
Be2
Cat Physics – another Donut Games game, nice Physic type game with good difficulty
Rainy Day -Free Run home avoid rain worth a try
Thief Lupin – Free
BMW M Meter – only useful to have fun in the car, see your 0-60 speeds and g-force
Light Bike 2
Puzzles
LetsTans – fit shapes into available space (dont play often but ok)
DragonsLair missed on the pc but I like the cartoon humour and simple quick time events
Doodle Fit – nice puzzle game fit shapes into other shapes
Rolo
Insanity
ZentomioLE
Word Games
Words with Friends
Befuddled
Moxie
iAssociate
Multiplayer Games
Depict (pictionary 8bit style)
Sniper (you vs another sniper)
StarPaga (space shooter in space ships)
Avoid (not my cup of Tea)
Tetris – no retro music, its ok but only get if cheap
N.O.V.A meant to be the best but I dont like FPS on the iDevices 
Trenches – Played for a while but this game get boring quick again not bad graphics or game play but better games for the money(Try stenches for free to get a feel)
Pixel Ninja
Capcom Game yes its streetfighter but a bad port
Bomberman – meh wish this was better version so much and where is the multiplayer
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