Romaji to hiragana converter
Note: Type words 'wa' and 'o' as 'ha' and 'wo', because that's how they are written in japanese.
If your text is ENGLISH, try english to romaji converter.
If your text is otherwise NOT standard romaji (but Finnish for example), use older converter instead.
Those two also offer katakana.
If you want kanji! Use the dictionary instead.
Written by Bisqwit (http://iki.fi/bisqwit/)
Disclaimer: The accuracy of the operation of this converter
is strictly limited to the progress of my Japanese studies.
Source code is available (php). It might interest you, as it is short (~340 lines (well, once was)), but contains hiragana encoding in iso-2022-jp, euc-jp, shift_jis and unihtml (without external programs), plus a quite elegant parsed table for romaji to hiragana conversion. It could be easily extended to support different romajizations, and has a theoretic support for katakana.