Your mention of a setting of Ubi caritas brought to mind the beautiful setting by the 20th-century French composer Maurice Duruflé.
The song Taste and see reminded me of another very beautiful a cappella anthem, O taste and see by Vaughan Williams.
Somebody mentioned Mozart’s Ave verum. I’d also suggest a wonderful setting of the same words by Elgar (who was of course a Catholic). To my mind, the simplicity of it is in some ways more reverent and mystical than the Mozart.
If you have a really good choir (and it does need to be really good!) I love Messiaen’s setting of O Sacrum Convivium! I find it a very profound meditation on the Eucharist.
If you have only organ available, another piece I love very much is Messiaen’s Le Banquet Céleste. Messiaen, of course, had a very deep Catholic faith, and this meditation on the heavenly banquet is wonderful. (I’m also a big fan of the piano work Vingt Regards sur l’enfant-Jésus, although I don’t know whether you’d use that for a wedding!)
I don’t know about where you are from, but in France a wedding (at any one in a church) is considered to be virtually in complete without a performance of Widor’s Toccata (Symphony for Organ No. 5 in F minor, Op. 42, No. 1, mvt. 5). I once heard a story about a French Catholic wedding at which the organist was taken ill during the service, and rather than allow the couple to leave the church without hearing Widor’s Toccata, the priest, who happened to be a decent amateur organist, played it for them.
I wanted to post links, but can’t as I am a new member.