I'm with Bleecker. Other than components, shoes and my best wool tights (which actually were like $80 in 1987 dollars
), I don't have much of anything on my bike that's over $100 singly. (If you add it all up though...
) I keep trying for a pair of expensive shorts (and actually committed to a pair not long ago), but so far my favorites are still the $80 Shebeest SSS.
A definite +1 on arm warmers, and this is the time of year for them - when it's too cold for short sleeves when your ride starts, and too warm for long sleeves by halfway. Knee warmers or leg warmers can be nice, too.
As far as accessories, I guess it would help to know what you already have. So far no one's mentioned tire inflation. IMO a pump is a necessity. It can be a full-sized frame pump if you have room for one, or if space is at a premium, a CO2 system plus a mini-pump for backup. Tire levers, spare tube, and patch kit for backup, and an under-seat pack to carry all that (plus whatever else you might want to put in your seat pack).
Speed comes from what you put behind you. - Judi Ketteler