I recently got a DS Lite too after trading in my PSP (No I didn't not want to hack it, knowing my luck I would just end up with what was an expensive paperweight, nor did I know anyone who could do it for me). So far my list of games are...
I would go with mostly everything everyone has said so far, I have been trying to get my hands on a few there that seem to be impossible to get here in Australia (at least on the east coast).
I might add, Ghost Trick is a wonderful game, if your anything like a mad gamer who can finish short games quickly and had bought it from a store which has a 7 day 'trial' who will allow you to swap for an equal to or less then game, grab it. Great story, good laughs, though sadly I finished in in one sitting (SUN RISE TO MIDNIGHT) with only a few sections of frustration (One due to slow thinking another due to slow response time.)...
Another that I just recently got my hands on is a game called Contact. So far its an interesting game, its kinda weird at the start and then slowly you get going, you have a character that levels up by doing, so moving around the map increases his agility and run speed, punching ups fists, clubing, blunt and swords up cutting skills. Its interesting, you also can apply 'stickers' which do things, what things you ask, donno not far into it, Just know I turned a cave full of Pigs into SKELETONS which surrounded my low level character. It was a, What does thi..... OH FUCK FUCK FUCK FUCK... moment...
Don't touch Final Fantasy: The 4 Heroes of Light. I being a good FF Fan... Hated this one. It started off ok. Nice story, introduced you to the characters, made a big deal about them. THEN BOOM!!! Lets split your main characters up, so now there is two over the 4 we promised you, and now here is the world, we will not tell you where to go in it, talk to some NPCs that give vague instructions but we won't tell you to do so (Thank god it was a staple of mine when playing RPGs) and then go to the east into that desert where every monster can be taken down in one hit because the monsters in the starting area near the boss could take you down in one hit, ha little grind there didn't ya. Oh and there is only one of them, so thats waste of times. Now go around the area in a certain spot which we won't really point out for you, find this key scene which contains nothing more then a "OH hey your going that way too, I will join you. Despite you don't know who I am, I am camped out in the middle of the desert at night with no tent and my face is covered so you can't see it..." And then go find another spot which you won't see until you stumble on it. And then go to a Tower which has as much dungeon design the putting the Great Pile of Endless Gold sacks at the FRONT DOOR! No it didn't, but I mean seriously, the first floor was a mass of Pillars with stairs in the four corners, wow. ITs amazing!!!