Romaji.org (Japanese -> Romaji Converter) : I usually romanize lyrics by myself, but sometimes I feel tired (or lazy). And that's when I go to Romaji.org. (^^) This nifty little site converts Japanese kanji into romaji!
To use the site, first you choose how you want the kanji to be formatted (I use the "separate text blobs" option, so the paragraphs/stanzas won't get broken into separate lines.) Then after you hit the "Click To Set" button, just paste your kanji lyrics and hit the "Convert" button.
Unfortunately, the converter does have a few flaws: it sometimes romanizes words incorrectly (ex: 君 is converted as "kun" instead of "kimi"). And it usually won't separate participles (ni, ga, de...) from regular words, especially if the word is written in hiragana instead of kanji (ex: ひとつで becomes "hitotsude", but 一つで is read as "hitotsu de").
But hey, if you just want romaji to sing to, this site is perfect. And if you know some Japanese (and have the actual song/MP3), you can easily clean the lyrics up yourself. ^^