Here's a nice punchy one - so short a post, it might even warrant now't more than a tweet, but the blog's been a bit barren of late so here I am.
When you're debugging code (of course that's a rare thing now I'm living the TDD dream ;), if you frequently find yourself digging around in the Visual Studio Watch or Quickwatch windows investigating properties on objects, sub-objects, sub-sub objects, etc, then here's a good 'un. The quickwatch window becomes massively more useful with one simple addition - override the ToString() method on every class in your system so that it summarises the key properties, without you having to expand that object and hunt down those properties.
For example instead of a list having a value of "Count = 5", wouldn't it be great to see "5 transactions totalling £300"? And when you expand that list of transactions, instead of "Transaction", isn't it better to see 5 objects that read things like "Transaction Value £100 - Authorised £150, Taken £150, Refunded £50"?
You can of course use this ToString() representation all over the place, you can use it in exception messages, logging, you can enter an object's name into the Immediate window to see it, etc. It ain't gonna change your life, but it makes my bug-fixing life just that little bit more tolerable.