Il Giardino Armonico has some excellent recordings of baroque music. I'm usually not a fan of period instrument performances, but this stuff really works for me. You still have to deal with the blatty horns, which I really detest, but the rest of it is great. Doesn't sound "thin" like some other period instrument recordings.

Their Brandenburgs are among the best I've heard, up there with Marriner. Here's a Youtube link to a performance of the fourth concerto, but that performance is unfortunately not nearly as good as the one on the recording.

They even bring something fresh and exciting to really tired old chestnuts. Their version of The Four Seasons is marvellous and unlike anything else out there. Check it out here, and compare with a more traditional (but still excellent) version (Itzhak Perlman with the Israel Philharmonic).

For an even more tired chestnut made fresh, see their version of Pachelbel's canon.