I love www.renshuu.org for vocabulary drilling. You can set up vocabulary quizzes from a number of different resources. Mine is set to drill daily, but you can set them up any way that works for you. I also use it to study kanji. Good luck with your studies!

www.memrise.com
I think that one is the best, because you can create mnemonics, in the form of pictures or just sentences, your own or use from others. That helps reminding words much faster. With that I needed just 4 days to learn all Katakana and Hiragana.

www.busuu.com
Not so good, but still, worth to take a look.

http://ankisrs.net/
Can be used on the phone as well.

http://www.guidetojapanese.org/learn/

How about this? http://anime-manga.jp/WordQuiz/LoveWordQuiz/ and this. http://nihongo-e-na.com/eng/site/tag/Vocabulary/

Sora = Sky Ningen = Human Hito = Person Same = Shark Yagi = Goat Neko = Cat Inu = Dog Raion = Lion Wani = Crocodile Densha = Train Jitensha = Bycicle Kuruma = Car Fune = Ship Hoshi = Star Bengoshi - Lawyer Sensei = Teacher Isha = Doctor Niku = Meat Yasai = Vegetables Terebi = T.V Mado = Window Ie = House Hai = Yes Iie = No Konnichiwa = Good Afternoon Ohayou Gozaimasu(Or for friends just Ohayou) = Good Morning Konbanwa = Good Evening Kokoro = Heart Atama = Head Ashi = Foot Hana = Nouse Kuchi = Mouse Me = Eye Te = Hand Zubon = Trousers Fuku = Clothes Denwa = Telephone Keitai denwa = Cell phone Yumi = Finger Yume = Dream Kaze = Wind Ame = Rain Kawa= River Tsukue = Deskopt Isu = Chair Tabemono = Food (Tabe= Food, Mono = Things) Nomimono= Drink I am learning Japanase too ;) Good Bye!

I recommend using a program called anki (can be found via Google). It's a way of managing flash cards on your computer. You can download Japanese flash card decks online and then anki will keep track of which words you have learned, which ones you are learning and so on. It's a really great tool for building vocabulary. I used it to learn 1 000 new words and phrases in just one month (about 30 - 60 minutes of studying per day).