One good stain that I know of comes from Sherwin Williams, the sell Wood Scapes or even Deck scapes will do the job, they both come in a Solid color or a semi-transparent shade, with plenty of choices in color. Both products come with a warranty for addes protection.
Cabot makes an excellent product for exterior use, including porch ceilings. Olympic and Duckback products are also good for this type of application. Avoid using any stains that are labeled for interior use and don't waste your money on brands like Thompson's Water Seal. This form a waxy build up that only lasts for a few weeks.
If you want a varnished look some good choices would be Messmer's Timberflex and McClosky's Man O War Spar Marine Varnish. Good penetrating stains would be Messmer's UV Plus and Superdeck transparent stain. If you want a semi-transparent or a solid stain then Cabot and Benjamin Moore both have a good selection of products.