To start with, remember that the equivalents of verbs which take for in English govern their own prepositions in Irish, and that you are supposed to learn the preposition with the verb. So, for instance, he is waiting for Seán is in Irish tá sé ag fanacht le Seán. This does not mean that le is particularly common as an equivalent for for, though.
But let’s get on with it. Here:
DO is typically used in the sense “to the benefit of”. Tá mé ag obair dó “I am working for him.”
AS is typically used in the sense “in return for”. D’íoc mé dhá euro as “I paid two euro for it”.
But note AR in the related but somewhat different sense in “I bought it for two euro”: Cheannaigh mé ar dhá euro é.
AR SON is usually used in the sense “for the sake of a noble cause”: Fuair Seán Ó Rudaí bás i bpáirc an áir ar son na hÉireann. “Seán Ó Rudaí died on the battlefield for Ireland.” It is a combined preposition that takes the genitive case, and when used with personal pronouns, you insert a possessive pronoun between ar and son: ar mo shon, ar do shon, ar a shon, ar a son, ar ár son, ar bhur son, ar a son. Note that in spoken dialects, the son part is often permanently lenited after ar, i.e. ar shon na hÉireann.
Note, though, that in Ulster Irish, ar son does usually have the sense “in return for, in payment for”. There, you’d say D’íoc mé dhá euro ar a shon. I guess that in Ulster, you’d use I bhFÁCH LE or AR MHAITHE LE when speaking about siding with causes or doing something in favour of somebody or something. In these expression, le is the normal preposition le and behaves in the normal way, as regards prepositional pronouns, mutations and stuff. (For your information: the prepositional forms of le are liom, leat, leis, léi – léithi in Ulster -, linn, libh, leo – or leofa in Ulster. Le becomes leis before the definite articles: leis an, leis na. And with the article it affects the noun in the usual ways.)
AS UCHT is usually used for “in return for”: go raibh míle maith agat as ucht do chineáltais “thank you a thousand times for your kindness”. It does find some use even in the sense “for the sake of” and “in account for”, but personally I’d prefer to use it only in the sense of “in return for”, and then only speaking about abstract things (i.e. I thank you as ucht your kindness, but I pay you as this thing I am buying).
LE hAGHAIDH is used in the meaning of “intended for”: Chuir siad seomra in áirithe le m’aghaidh “They reserved a room for me”.
IN ARAICIS is typically Ulster Irish, and it is used when you go, say, to the airport or the railway station “for” somebody, i.e. to meet and fetch this person. Chuaigh siad go stáisiún na traenach in araicis Sheáin “they went to the railway station for Seán”. Takes genitive, or personal pronouns. I guess that in the standard language you use i m’araicis, i d’araicis, ina araicis, ina haraicis, inár n-araicis, in bhur n-araicis, ina n-araicis, but the first two ones are in m’araicis, in d’araicis if the orthography tries to imitate genuine dialectal pronunciation.
I gCOMHAIR or FAOI CHOMHAIR is basically synonymous with LE hAGHAIDH, i.e. intended for. Use genitive, or personal possessive pronouns when appropriate: i mo chomhair, i do chomhair, ina chomhair, ina comhair, inár gcomhair, in bhur gcomhair, ina gcomhair; faoi mo chomhair, faoi do chomhair, faoina chomhair, faoina comhair, faoinár gcomhair, faoi bhur gcomhair, faoina gcomhair.
AR FEADH (I tend to write it ar feádh, but I see that the standard orthography is ar feadh with no fada. Oops.). This one is mostly temporal: ar feadh lae, ar feadh bliana and so on – “for the duration of a day, a year”…
THAR CIONN. Well, the standard is again thar ceann, but in my opinion it is entrenched enough to use the old dative form here. This means “on behalf of”, i.e. as a representative for. Shínigh an Príomh-Fheidhmeannach an conradh thar cionn Bigmoney Teoranta. “The Chief Executive Officer signed the contract for (on behalf of) Bigmoney Ltd.” Takes genitive (thar cionn na cuideachta) and personal possessive pronouns (thar mo chionn, thar do chionn, thar a chionn, thar a cionn, thar ár gcionn, thar bhur gcionn, thar a gcionn).
FAOI DHÉIN when you go to the shop “for” something, or when you go and fetch somebody from the airport or the railway station. Chuaigh mé go dtí an siopa faoi choinne uachtar reoite = I went to the shop for some ice cream. Takes genitive, and personal possessive pronouns (faoi mo dhéin, faoi do dhéin, faoina dhéin, faoina déin, faoinár ndéin, faoi bhur ndéin, faoina ndéin).
FAOI CHOINNE is for a particular kind of use, for an occasion. Cheannaigh mé cóta te faoi choinne an gheimhridh = I bought a warm coat for winter. Takes genitive, and personal possessive pronouns (faoi mo choinne, faoi do choinne, faoina choinne, faoina coinne, faoinár gcoinne, faoi bhur gcoinne, faoina gcoinne).
DE GHRÁ is used typically with abstract nouns in the meaning “for the sake of…” (de ghrá na síochána = “for the sake of peace”, for instance). Takes genitive.