Oh well, I figure I'll just jump into the bandwagon.
Hello, my name is Kurrus and I joined this forum to express my love for Spelunky.
As much as I love Spelunky, though, I still feel there's room for improvement, apart of all those much needed bugfixes so many people have requested already. (bugged trees

)
So here's a bunch of suggestions!
1.- A "treasure" room of some sorts, that keeps track of the money you've collected and the monsters you've killed. However, it should keep track of the total of money and monsters, not just the highest amount, as the Scores screen does.
2.- Making the woman restore
your health fully two health points if you carried her to the exit without dropping her even once would be an interesting challenge.
3.- I think this has been suggested already, but basically, make the title screen change graphically according to your stats. For instance, making candles or gravestones appear if you've died a lot of times, or making the Spelunky letters be golden if you've collected a lot of money.
4.- I haven't got a name for this, and it's a bit hard to explain. There could be a series of hidden "achievements" in the game, like killing a certain amount of enemies, or completing a level in a certain time. You'd get no notification of them when you get them, but they'd trigger objects (trophies, medals, you name them) to randomly appear in crates, chests, or inside the dirt ready to be blown by a bomb. If collected, they'd appear in the treasure room, and reveal what the "achievement" was.
That's all for now I guess.
Spelunky is great, keep up the good work!
EDIT: dang, just as I post this, someone suggests basically the same as me. Yay, mind powers! :D
EDIT 2: the fine lad that posted after me revealed an interesting piece of information, which I took and put here. Thanks!