I think people are missing a trick by not looking at cases you can get for the Gameboy Advance - they've dirt cheap, and all of 'em will fit an SL5xxx, and some fit the SL6000 as well.
I mostly use a cheapie own brand leather case from Game (used to be EB) for my SL5500:
[img]http://angela1.data-uncertain.co.uk/~zaurus/CasePhotos/leatherClosed.jpg\" border=\"0\" class=\"linked-image\" /]
[img]http://angela1.data-uncertain.co.uk/~zaurus/CasePhotos/leatherOpen1.jpg\" border=\"0\" class=\"linked-image\" /]
[img]http://angela1.data-uncertain.co.uk/~zaurus/CasePhotos/leatherOpen2.jpg\" border=\"0\" class=\"linked-image\" /]
It's a perfect fit for a SL5500, and has a pocket for your extra SD/CF/Wifi/etc. Cost about £5 (or $8 for the folks in the US).
I've also got a Gameboy Advance belt pouch/holster. I think my son bought this for me from Toy's-R-Us. It's actually a bit big for the SL5500, so the 5500 fits in with it's WIFI card still in the CF slot. But handily, with it being that bit bigger, it actually fits the SL6000 perfectly (not shown - my wife's hidden the SL6000 'coz it's my christmas present).
[img]http://angela1.data-uncertain.co.uk/~zaurus/CasePhotos/holsterClosed.jpg\" border=\"0\" class=\"linked-image\" /]
[img]http://angela1.data-uncertain.co.uk/~zaurus/CasePhotos/holsterOpen.jpg\" border=\"0\" class=\"linked-image\" /]
[img]http://angela1.data-uncertain.co.uk/~zaurus/CasePhotos/holsterBack.jpg\" border=\"0\" class=\"linked-image\" /]
Again, it's got an internal pocket for your extra SD/CF cards, and also has a belt clip (velcro'ed at on end to clip over your belt). I think it cost him about £4 ($7 ish).
The holster looks a bit battered in the photos - that's from it's time holding my GBA on various beachs around the world (Antigua, Koh Samui, Brighton...).