Kiddushin, Chapter 2, Mishnah 9. This mishnah lists items that are forbidden to derive benefit from, items from which no monetary value can be obtained, and therefore one who uses them as the means of betrothal has not effected a valid kiddushin.
The items forbidden for benefit listed in the mishnah:
"HaMekadesh ba'orlah" - the fruit of a tree during the first three years after it is planted, which has the status of orlah. It is forbidden to derive any benefit from it, so no value can be obtained from it.
"B'kil'ei hakerem" - wheat, or any other crop besides grapes, that grew in a vineyard and became forbidden once it reached a certain stage of growth.
"B'shor hanniskal" - an ox that gored and thereby became liable to death, which halachah requires be put to death. Even if it was properly slaughtered, it remains forbidden for benefit.
"B'eglah arufah" - the calf whose neck is broken when a murder victim is found and no one knows who struck him, and the city nearest to him breaks its neck. The prohibition of benefit takes effect even before the neck is broken, from the moment the calf is brought down to the rugged valley where the ceremony takes place.
"B'tziporei metzora" - the two birds used for the purification of a metzora: one of them is slaughtered, and the second is used for sprinkling the blood and water on the metzora and is afterward set free. The bird that is slaughtered is forbidden for benefit.
"B'se'ar nazir" - a nazir who completes the days of his nezirus shaves off his hair, and that hair is burned beneath the pot in which his shelamim offering is cooked. The hair is forbidden for benefit.
"U'v'peter chamor" - the firstborn donkey, the only non-kosher species to which the law of the firstborn applies. The mitzvah is to redeem it with a lamb, and if it is not redeemed its neck is broken, and therefore it is forbidden for benefit. Some hold that the prohibition of benefit applies only after the neck is broken, and others say that it applies even before that, as long as it has not been redeemed.
"U'basar b'chalav" - the prohibition most familiar to us: meat and milk cooked together, from which it is forbidden to derive benefit.
"U'v'chullin shenishchetu ba'azarah" - an animal that was not consecrated as an offering and was slaughtered in the courtyard of the Beis HaMikdash is forbidden for benefit.
"Ein hamekadesh bahem": one who betroths a woman with any of these - she is not betrothed, since anything forbidden for benefit has no monetary value.
"Mecharan v'kiddesh b'damam - mekudeshet":
Admittedly one should not do this in the first place, but if he sold one of these items and betrothed a woman with the money he received for it, she is betrothed. The reason is that with each of these items the prohibition of benefit does not transfer to the money, but rather remains with the item itself. The money is therefore permitted for benefit, it belongs to him, and it has the power to effect kiddushin.
The only items forbidden for benefit about which it is said "tofes damav" - that whatever is received in exchange takes on their status and becomes forbidden as well - are the produce of the seventh year and objects of idolatry, and these are not listed in our mishnah. With all the other items listed here the prohibition of benefit does not transfer to the money, and therefore kiddushin performed with that money is valid.
In summary: this mishnah lists nine items forbidden for benefit - orlah, kil'ei hakerem, the ox that is stoned, the eglah arufah, the birds of the metzora, the hair of a nazir, the firstborn donkey, meat cooked with milk, and non-consecrated animals slaughtered in the courtyard - and one who betroths with them has not effected a valid kiddushin, because they have no monetary value. But one who sells them and betroths with the proceeds - she is betrothed, since the prohibition of benefit does not attach to the money, with the exception of the produce of the seventh year and objects of idolatry, which are not listed here.