I mentioned translit.ru in a comment this morning, and michael farris said it should have its own post, so here it is. You just type English letters into the box (abcde) and Russian letters appear (абцде). As you see, c gets you ц, and you can use w to get щ (though shh will also work; it collapses sh, ch, zh, etc. automatically). I’ve used it every day since frequent commenter Tatyana told me about it. Thanks again, Tat!