Saru Getchu! (Ape Escape) requires the twin sticks... how else can you catch the monkeys? Other than that I can't think of any off the top of my head. A lot of games really benefit from it though, so it'd probably be nice to have them.
If you dont want to use the joysticks, use a psx controller and mount it in the case. If you do want analog sticks, mount it in the controllers case on the outside of the case. Worked well for me.
A hack I saw somewhere said you could turn D-Pad signals into Analog Stick with a switch, sorry, but I forgot where, just tell you to show you its possible, so someone may use it in a portable.
Somebody please buy my Dreamcast >_> £20+shipping