I use the Topeak Aero Wedge Size Medium and it fits everything I need perfectly. I think it is a good size too. Doesnt make the bike look wierd and holds what you need. I got the version that velcros ont he seat rails instead of the clips because I prefer the velcro as those clips always break. My only complaint is that the strap that goes around the seatpost is huge. Its made for like a 1.5" - 2" seatpost and is loose on my seatpost but it hasnt caused any problems.