The "Stack Exchange" menu button in the top bar is actually a link to http://stackexchange.com/.
Normally, clicking that button just opens the site switcher menu. But on Firefox (at least), if you middle-click the button, it will act like a normal link, and open http://stackexchange.com/ in a new browser tab. (Of course, right-clicking and using the context menu will work, too.) From there, you can get to meta.SE using the same site switcher menu in the normal way.
Of course, this is kind of a hidden feature, but it can be handy if you know about it. Alas, it turns out that it's also browser-dependent; on Chrome, middle-clicking just opens the menu. :(
Ps. If you want to go directly to meta.SE, you can find it in the site switcher menu itself by typing "meta" into the search box:
As Al E. notes, you can also add it into the customizable "Your Communities" section of the menu (by clicking the edit link), so that it's always just one click (well, two clicks — you need one to open the menu in the first place) away.
Also, you don't need to go to meta.SE to report bugs; the SE dev team does track bug reports on per-site metas. If the bug seems to only appear on a specific site, it's usually best to report it on that site's meta; for bugs that affect multiple sites on the SE network, meta.SE is indeed the right place. Either way, though, as long as you use the bug (or feature-request) tag, the devs will notice it.