I'll second the suggestion for Epifanes Wood Finish Gloss. It is very easy to apply (sanding between coats is optional if re-coated within 72 hours) and I found the finish to be excellent. I also applied it to mahogany.
It stood up to 12 months in the Louisiana sun before I put on a few maintenance coats. However, the finish looked great even after the full year.
You can also build up with the WFG and do the last couple of coats with a more traditional varnish.
Here's a photo of the varnish on my companionway boards as I neared the final coats: