<p>I want to write an Add-In for Visual Studio that provides instant search for the solution explorer. So you press a key combination and while you are typing a list first containing all files of the solution explorer gets narrowed down.</p>

<p>But how can I get access to the solution explorer using C#? Does anyone have some good resources?</p>

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<p>Edit: I edited the title, so that it more relates to the content, since all of you posted already made plug-ins.</p>

Why re-invent the wheel? DevExpress + Microsoft tied up to offer
CodeRush Express
for free @ PDC2008 that does just that if I understand you correctly.
AFAIR I think the magic key combo for Jump to File is Ctrl+Alt+F and it does substring matches too. I tried it and it worked for me. Pretty nifty. Here's
the link
to a recording in case I goofed up on the actual keystroke... some really nice tips in it.
Update
: Wrote
a blog post
for those who're short of time.