Sent is a Gmail client for iPhone that's decidedly more native than Google's own, still disappointing Gmail app. It also offers multiple account support. But before you get too excited it's $4.99 and doesn't offer push notifications (yet?). It also asks you to login to your Google account right inside the app, rather than sending you to Google's web page for authorization. Maybe that doesn't work for 3rd party clients, but it does work for my security paranoid brain that flinches at the thought of putting my creds into 3rd party app. The internet birthed Xauth for a reason, after all.
Whether you like the idea of a separate app for Gmail or not -- and I personally don't -- it would be nice to see Google take some of their search billions -- nicely fed by iOS devices, thank you! -- and make the first party app a lot of people are still waiting for.
$4.99 - App Store link