Okanagan University College Pronunciation
http://www.faceweb.okanagan.bc.ca/pron/
This has some really useful minimal pair exercises. For example, if you still have problems with /r/ and /l/ you can hear and practice words with them in. There are also dictation exercises. Have fun with the tongue twisters to practice the sounds.
Sounds of English
http://www.soundsofenglish.org
A good site which teaches you American pronunciation. It includes some videos showing how to pronounce words and has some useful exercises on word endings.
