The Times has a crossword club, where, for a yearly subscription you can solve and submit all their crosswords online. The Telegraph also has this facility, but only for selected crosswords, and you have to print them off and submit them by post. I used to subscribe to both, but cancelled the Telegraph recently in favour of The Times. You also get the newspaper every day to read online, a bargain at �25 per year.
Surely One Across, it is so well known! Sometimes gets busy, but you can get a hell of a lot of answers simply by entering the word you need with a '?' for missing letters!!