I have just found very useful page on MSDN: 101 Linq Samples. Should be very useful reference for lots devs.

Here's just a quick copy-paste:

##### Restriction Operators

##### Projection Operators

- Select - Simple 1
- Select - Simple 2
- Select - Transformation
- Select - Anonymous Types 1
- Select - Anonymous Types 2
- Select - Anonymous Types 3
- Select - Indexed
- Select - Filtered
- SelectMany - Compound from 1
- SelectMany - Compound from 2
- SelectMany - Compound from 3
- SelectMany - from Assignment
- SelectMany - Multiple from
- SelectMany - Indexed

##### Partitioning Operators

- Take - Simple
- Take - Nested
- Skip - Simple
- Skip - Nested
- TakeWhile - Simple
- SkipWhile - Simple
- SkipWhile - Indexed

##### Ordering Operators

- OrderBy - Simple 1
- OrderBy - Simple 2
- OrderBy - Simple 3
- OrderBy - Comparer
- OrderByDescending - Simple 1
- OrderByDescending - Simple 2
- OrderByDescending - Comparer
- ThenBy - Simple
- ThenBy - Comparer
- ThenByDescending - Simple
- ThenByDescending - Comparer
- Reverse

##### Grouping Operators

- GroupBy - Simple 1
- GroupBy - Simple 2
- GroupBy - Simple 3
- GroupBy - Nested
- GroupBy - Comparer
- GroupBy - Comparer, Mapped

##### Set Operators

##### Conversion Operators

##### Element Operators

- First - Simple
- First - Indexed
- FirstOrDefault - Simple
- FirstOrDefault - Condition
- FirstOrDefault - Indexed
- ElementAt

##### Generation Operators

##### Quantifiers

##### Aggregate Operators

- Count - Simple
- Count - Conditional
- Count - Indexed
- Count - Nested
- Count - Grouped
- Sum - Simple
- Sum - Projection
- Sum - Grouped
- Min - Simple
- Min - Projection
- Min - Grouped
- Min - Elements
- Max - Simple
- Max - Projection
- Max - Grouped
- Max - Elements
- Average - Simple
- Average - Projection
- Average - Grouped
- Fold - Simple
- Fold - Seed