Ideally you'll use the sealant bafore the carnauba detailer so as not to affect the sealants bonding to the paintwork.
There are alot of sealants about now and I'm sure Davidg will be along to recommend his as well but, I'll list the popular one's I have:
Serious Performance Polymer Super Sealant - £8.95 - Nice clear, wet finish. Slick to touch and very good durability.
Duragloss Total Performance Polish - £12.49 - Very wet finishing and has been the 'en-vogue' sealant this year in the States with forums like Autopia.
Duragloss Clear Coat Polish - £8.95 - Gives a deeper gloss finish compared to the TPP above. Definately benefits from using the Polish Bonding Agent Duragloss do as well. Cheaper price but is 236ml compared to all the others which are 500ml. You get a shampoo sample and an applicator in the box too.
Prima Epic - £14.95 - A deep, clear finish from the Epic. Good durability and very easy to use.
Four Star UPP - £14.95 - Very bright finishing sealant and still a fave on lighter colours if you want a very reflective finish. Not the longest lasting sealant but, one of the slickest.
Hope that helps a bit!
Cheers
.