The algorithm of choice is two rounds of SHA256, which has completely arbitrary outputs and a massively unsearchable output space. To this end, there is no data mining or valuable calculation actually being done. Here's what's really happening:
Every so often, the rules of the Bitcoin protocol set a difficulty number. This number sets a sort of target for a value miners are looking for. Since the output of SHA256 is essentially random with respect to its input, miners are all just looking for some random value in a given field that makes SHA256(SHA256(x)) return a value within a specified range. Such a value is considered a "solution" to the mining problem, but really it's less like math and more like throwing darts while blindfolded until you hit the bullseye. The changing difficulty number ensures that block solutions will be found at regular intervals no matter how many people are mining.
This solution does not hold any valuable data or information of any kind, except that it proves that someone somewhere had to have done a lot of work to find a value that produced the desired output. This also means that for someone else to fake that data they would also have to do a lot of work.
Since each block of data references the block before it, these hashes - and the work it took to create them - also stack up, meaning that older data would require a TREMENDOUS amount of computational power to falsify, since you'd also have to falsify every block that came after it, faster than the entire network combined is solving new blocks. This is the entire underlying security mechanism of Bitcoin: Data in the Blockchain represents a consensus and this is the way a network of people with no other trust mechanism reach a consensus.
This is likely why you've had such a hard time finding an answer to your question: There isn't anyone you're solving algorithms for and the only "why" is "because it's hard work, and fraudsters would have to do more hard work than everyone else combined to lie to the network."
Finally, as to the "someone thinks this is worth a lot of money" - there are two sources of mining income. The first is transaction fees paid by those whose transactions are in the mined blocks, which seems pretty reasonable given that the miners' work is the only reason that data will be trustable. The second is the block reward.
One of the more difficult problems to solve when decentralizing a currency is deciding who gets the initial run of the stuff. In this case, it was decided that the miners who are doing valuable work to secure the network should receive that initial issuance, in the form of a "block reward." Every so often this reward is cut in half and eventually it rounds down to zero. At that point all 21 million bitcoins that will ever exist will have been mined and the only reward miners will continue to receive is the transaction fee.
Just to give an example for those sheeple who gave me negative feedback for asking a question - if some stranger came up to you and asked you to deliver a package for $1,000 to another stranger, and when asked what was in the package, just replied with "stuff - it doesn't matter" would you deliver it? Who knows what you're doing or what the reprocussions are? This "blind trust" mentality is disconcerting to me in an age when rampant identity theft, privacy infringements, and hacking are on the rise – Claire Mayo – 2014-08-19T01:03:29.577
I don't see how your package delivery analogy relates to your question. Are you asking how do you know the solution found isn't useful for something else? – greatwolf – 2014-08-19T05:43:56.080
3Undid the downvote: found the question legit, though a bit conspiranoic. The software is open source, so to keep with your analogy the package you're asked to deliver is made of transparent plastic so you can clearly see to the content: paper sheets with long excerpts from accounting books, listing inputs and outputs plus a final set of seemingly-random numbers. Plus, from time to time, the recipient just throws it into the garbage bin right away saying "thanks, but too late" (and then refuses to pay you, the darned!) – Joe Pineda – 2014-08-19T22:37:03.750
Good analogy Joe – Wizard Of Ozzie – 2014-08-26T01:57:16.420