I see a lot of this kind of thing when reviewing code.

Dictionary<string, SomeType> _dictionary = new Dictionary<string, SomeType>();
_dictionary.Add(key.ToLower(), someInstance);

// and elsewhere in the class
SomeType someInstance = _dictionary[key.ToLower()];

It's nice to see people worrying about case insensitivity (provided that's what you want) but there's an even better way to do it. You can specify a comparer in the constructor of the dictionary like so:

Dictionary<string, SomeType> _dictionary = new Dictionary<string, SomeType>(StringComparer.InvariantCultureIgnoreCase);

In this case we're using the case insensitive invariant culture string comparer provided for free on the StringComparer class.