Frank Daulton has kindly allowed me to put up his lists of the English-Japanese loanwords which appear in the top 3000 most common words in English.
The General Service Word List is here last time I looked. The full scanned GSL list is available from this site. Kudos to the scanners!!!!!!
If you need to get objective frequency data you can download the HUGE British National Corpus. This stuff is for techies and vocab nuts. Not for the faint hearted, but brilliant stuff. I do not advise this unless you are going to stick it in a database to search. It will take up over 50MB of your hard drive. The lists here DO NOT give actual frequencies per word. For that information you must refer to Carroll et al's Word Frequency Book and its ilk or get list of words with actual frequencies per word ordered alphabetically or numerically you could download the HUGE files from the British National Corpus archives. There is also a wordlist (4MB) from the BNC on Mike Scott's website too for download.
You can download many individual lists from here.
You can also get similar information from COBUILD 's Bank of English. No word lists are available.
If you are looking for a text (say an old book) for corpus work then the Oxford Text Archive is the place to be .
Another place to look for word lists is Tom Cobb's Compleat Lexical Tutor page
The Academic Word list by Averil Coxhead is here. (It replaces the old University Word List)
The Oxford 3000 list is here (based on the BNC). Here are some sub-lists from the Oxford 3000. Language study terms | Arts words | Science words | Business and finance words.
Multi-concordancer for comparing texts
Paul Nation's RANGE program is here.