Here are some helpful websites for accents!! Right now most of them are for Irish and Scottish. I’ll add more to this whenever I come across something useful.
Scottish Sayings and Slang – http://scotlandwelcomesyou.com/scottish-sayings/
Irish, Scottish, Cockney Rhyming Slang, and other fun translators – http://www.whoohoo.co.uk/main.asp
*Note* I use this to help set up an idea of phonetic spelling for Irish and Scottish accents, but don’t use as an exact form!
Lowland Scot Swear Words – http://nawcom.com/swearing/lowland_scots.htm
Celtic Deities and Mythic Figures – http://www.terrapsych.com/gods.html
*Note* Sometimes going to the culture itself is very useful.
Need A Name with Meaning? – http://www.behindthename.com/
The Speech Accent Archive – http://accent.gmu.edu/
*Note* This is real technical and without some understanding of phonology this site can be confusing. I suggest looking up the basics on phonology first to get a general idea. For me, I took a class in college. It was actually fun! I may or may not make a post about phonology. If there is anyone interested, let me know.
Youtube! I strongly suggest searching for real speakers of the accent you want to mimic and listening to them. For Irish I used this wonderful gal Lainehh as a reffereance. Not only is listening from the source better, but can be quite intertaining (you are a very funny girl Lainehh and injoyed watching you!) – https://www.youtube.com/user/Lainehh