The ones NOT to download cause they are useless or might cause problems? That's up to your preference.. there are some pretty lame things out there.. but they might be dumb to me, but great for you... just search out and read what they all are and what they offer...
Okay... why don't you just read some about what applications are out there? Jailbreak your phone if you want to (if you don't, you'll need to wait until the SDK release to add apps), then try things out to find what you like. No one can tell you what is or isn't "lame" or "stupid."
It would be a less confusing question if you just asked "what are the best apps for my new iPhone?" or something. You had a lot of us scratchin' our heads
Once you get your iPhone do NOT install these:
BSD, SSH, Summberboard, Customize, iAno, Pocket Guitar, Drummer, iPhysics, TapTap Revolutions, Camera Pro, iZoo, Ipac3D, Yeti3D, or even iSolitaire.
All of these apps can turn you into a raving iPhone junkie that spends all day playing with your phone instead of doing productive things like cleaning your house or even going to work. Stay away from anything that is remotely fun and only install boring programs like pong or iLevel (if you don't know what iLevel is, look it up, it's a hoot).