Udo, just this morning I was trying to find an old thread in which we discussed precisely this. I think the general consesus was that "in the market" is better than "on the market". Can someone find this thread?

I'm not a businessperson, but off the top of my head, I'd say a company or a person tends to be *in* a market, whereas a product tends to be *on* a market. The prepositions become into and onto respectively whenever movement is involved, just as in other situations analogous to the accusative.

This seems to be the old thread, but it doesn't look all that conclusive:
related discussion
Both "introduce into" and "introduce onto" sounded a hair odd to me, but maybe more because of "introduce" than because of the preposition. I might have just gone for "bring X onto the market" in the case of launching a new product.

One other mention of "on the market" (there may be others I didn't find):
related discussion


Other examples:
They decided to bring the new printer onto the market next spring.
The new printer isn't on the market yet; it's coming out in spring.
You'll have to put your house on(to) the market if you decide to move. ["onto"/"into" are often just "on"/"in" in everyday speech]
The house was on the market for months before it finally sold.
The Sony format won out because it came onto the market first.
When several formats are all on the market at once, one eventually wins.
Many new high-tech stocks came onto the market in the same quarter.
When there were too many high-tech stocks on the market, prices dropped.

IBM has been a leader in the computer market for decades.
Kodak is trying to break into the digital-camera market.
The costs of entering (getting into) a new market can be steep.
When companies compete in a new market, consumers often benefit.
The young trader wanted to become a major player in the stock market.
The young trader was hoping to break into the stock market.

However, now that I've ventured a guess, I fully expect to see examples that shoot down my hypothesis... (-:

Just to wrap up Udo's question, "at the market" sounds to me like a literal place where you shop: the supermarket, the flower market, etc. The corresponding preposition for movement would then be "to." E.g.,

I went to the market to get flowers and something for a vegetable course.
We saw him at the market. He was buying steaks and a bottle of wine.

This little piggy went to market,
This little piggy stayed home;
This little piggy had roast beef,
This little piggy had none.
And this little piggy went "wee wee wee" all the way home.

(Traditional children's verse. Each piggy represents a toe, starting with the big toe and ending with the smallest one.)