One of the ways I get my brain up and running in the morning, now that I'm retired, is to do the Code-Cracker. My mother, when she was alive, and was living upstairs in our house, used to have the Code-Cracker done before I got out of my heated blanket in the morning (and I've always been an early riser). Suffice to say, her brain was pretty sharp too.
I got started on the Code-Cracker in my last job - one of the female staff always used to do it in the morning tea break, and so we'd make a copy of it and both of us would get on and do it. I never managed to finish it before she did! I doubt that I would have beaten my mother either, if she and I had had a race. (She could do cryptic crosswords without having the puzzle in front of her, just by having someone tell her how many spaces there were and what ones were filled in.)
The Code-Cracker that appears in the Otago Daily Times is produced by Simon Shuker, who lives in Wellington, NZ. It's reproduced throughout the country in various papers, and is one of the most popular daily puzzles available. And it's popular not just in this country, but in a wide variety of places around the world - it appears under the name Codeword in the Daily Mail in London, for instance, where it's been appearing for two decades.
Unlike some versions of Code-Cracker, Shuker's one always uses all the letters of the alphabet. Furthermore, it's laid out in such a way that you can quickly see whether you've already used a particular letter or not, and what number it relates to. And the numbering starts from the first box on the page and works consistently through the puzzle: before number 26 appears all 25 other numbers will have turned up in sequence.
Some versions of the puzzle don't use all the letters of the alphabet, which is frustrating, and some of them jumble the numbers all over the place, so it's not easy to know where you're starting from. Personally, I think Shuker's 'hand-crafted' puzzle is the best version available - and if doing one a day isn't enough for you, you can always buy a book of his pre-published puzzles and do them again...
You can find a couple of interactive samples on the Code-Cracker site. However, I notice that if you click on one of the letters at the bottom all the places that letter appears will show up. That reduces the puzzle element considerably. Think I'll stick to the paper version!