Launched last month, the Adroit Switchblade for Xbox 360 from EvilControllers resulted after a tie-up with AbleGamers. It's got a lovely mix of accessibility features such as remote rumble packs you can position anywhere (a bit like the Rez Special Edition "Trance Vibrator" for PS2 Rez but should work on all games). It has split modules for the left and right thumb sticks (a bit like the HORI Separate controller but more versatile). It has latching functionality built-in (cheaper than buying external latching switches which my C-SID relies upon). It has three different set-up profiles that can be triggered by a single switch (like JoyToKey on PC).
It comes in at about £266 + import tax in the UK. In comparing the Adroit Switchblade to it's nearest price rival, my C-SID I see things as follows: In the UK, The C-SID is going to work out about £50 cheaper. The C-SID is not available outside of Europe. The C-SID can connect to all the modern platforms and PC/Mac as the Switchblade can plus Wii (classic controller games only such as Mario Kart), fat PS2, Xbox, Dreamcast and Gamecube. The Switchblade has a single switch switchable profile system for the Xbox 360, the C-SID can only do that on PC). The Switchblade has latching features built in, you need to purchase external latching switches for the C-SID. Both allow for team-play on an Xbox 360 with a secondary standard controller (so I'm told), but on the C-SID you can also use a keyboard if helpful.
If you're thinking of buying a switch interface, more food for thought can be found at the Accessible Gaming Shop. The Adroit Switchblade is definitely good news for choice in game accessibility.