Different languages generally have different online dictionaries. For German, I often find myself using dict.cc, whilst for French, I use Reverso. The best way to find dictionaries is to Google, but one option to definitely consider is the ever-growing Wiktionary. Effectively every language has a Wiktionary and whilst it can be difficult to navigate, it is quite large and the range of languages makes it amazing.
Verbix is another web-based tool. It allows you to conjugate verbs, and even supports irregular ones.
The free web-based tool supports verb conjugation in 97 languages, ranging from Afrikaans, to Milanese, to Old English to Welsh! They offer Windows shareware which supports over 300 languages.
Verbix also offers a tool too which analyses text and guesses its language.
Podcasts are a very useful way to perfect your listening.
It is very useful for me to hear a native German or a Francophone to speak.
Browsing iTunes will obviously bring up many possibilities.
My suggestions? For German, use Slow German. For French, try One thing in a French day. Naturally, I can’t make suggestions for other languages!
One of the best ways to learn is purely to repeat.
Many vocabulary trainers are available. These allow you to input words, or use preprepared word lists, and then be tested on them. The trainers compile statistics so you can identify weak points etc.
For OS X, try the freeware Vocab. A wide-range of options exist for Windows users; ProvaLingua seems popular. Another option, which also works under Linux, is this program.
I already mentioned that Wiktionary exists in many languages, but so does Wikipedia.
To improve your knowledge of a foreign language, try reading an article on your native language Wikipedia and then on a foreign one. It won’t be the same word for word, but many ideas will be similar so you should be able to pick out some key words.
Wikipedia is also a good way to find technical vocabulary in a foreign tongue.