Recs.
Updated
A managed version exists: C#-SQLite, it's a port to managed C#, so it can be run as AnyCPU.
Read article Comparison of SQL Server Compact, SQLite, SQL Server Express and LocalDB.
SpecsUpdate
Pros
Pro Portable
SQLite is a file-based database. It works by sending requests to a single file where all the data is kept instead of communicating with a hosted database which gives access to an interface by making use of sockets and ports.
This makes SQLite extremely portable throughout different applications, all that's needed to transfer the whole database is to make a copy of the file.
Pro A powerful ORM can be found in SQLite-net
SQLite-net is a powerful ORM that allows .NET applications to store data in SQLite databases. This tool makes it easier to integrate SQLite with .NET development.
Pro Great language support
SQLite has bindings for a large number of programming languages, including BASIC, Delphi, C, C#, C++, Clipper//Harbour, Common Lisp, Curl, D, Free Pascal, Haskell, Java, JavaScript, Livecode, Lua, newLisp, Objective-C (on OS X and iOS), OCaml, Perl, PHP, Pike, PureBasic, Python, R, REALbasic, REBOL, Ruby, Scheme, Smalltalk, Tcl, Visual Basic.
Pro Great for testing and first stages of development
Because of it's ability to scale and with the portability that a single-file database gives you without losing much of the power and features that SQL gives developers, it's a great choice for testing applications and for the early stages of development when the workload and the data that needs to be stored is not that large.