Gresp15C

Oh, the other thing: Studded tires for the winter bike.

Scummer

Ortlieb Rollers and hub dynamo driven front- and taillight. Hands down.

Saving Hawaii

Busch & Muller Ixon IQ Premium - $100
Wahoo RFLKT+ - $80

There are others I use but those are the only two that stand out to me as excellent value/price. The light does such an excellent job compared to all others that I have including much brighter ones. The RFLKT nails its job and saves my phone battery. Heads up that the RFLKT I got almost got returned for initially abysmal battery life (two batteries in two weeks). This was resolved with a firmware update. I haven't changed the battery since.

b_young

Already mentioned but I'll put another plug for Air Zounds. Cars do not expect a bike to sound that loud. It gets their attention and usually makes them laugh.
Lights--I don't care what kind and you can never ever have too many.
Other than that the Topeak bag and rack with locking track system is the best.

Chucka

mountainsmith fanny pack - 25 years ago. Still use it for food / keys... All the zips still work, no reason to buy a new one.

DiabloScott

I only use the lights in winter, and I take my fenders off in spring.



But I use my Ibera rack and trunk bag every time, year round.

Chucka

mountainsmith fanny pack - 25 years ago. Still use it for food / keys, shirt shoes... All the zips still work, no reason to buy a new one. Looks dumb but comfortable

dailycommute

Number one commuting items for me (and any bike ride for that matter) are mirrors. I have found them the most useful items hands down over the years. It is hard to be a defensive commuter on highway traffic corridors without mirrors. Of course I always wear a helmet and carry spare tube/pump/levers. Also only commute on brooks saddles these days.

Matt144

#1 - My Two Wheel Gear commuter bag
#2 - PDW rear light

Those are the two things that have exceeded expectations and made my commute much easier and safer.

Darth Lefty 

Rack, tail bag, lights. I use other stuff too but those are the important ones. I'd add fenders except that we get 300 days a year of fair weather.

InTheRain

You're right! I had completely forgot about mirrors. I guess I take them for granted. I bet I haven't ridden a bicycle without a bar mounted mirror for over seven years. I bet i check them once every few minutes, and several times in a 30 second span of time just before I "take the lane." Excellent, excellent point! I think they should be at the top of every commuters list.

Andy_K 

I've got seven bikes, most of which have been built from parts. Which parts depends on what the bike is for, but I'm definitely noticing some recurring themes.

1. Thomson seat posts -- Really any seatpost with a two-bolt mechanism is fine. I've got three that aren't Thomson, but Thomson are very nice, so I've got four of those.

2. Specialized Phenom saddles -- Obviously saddles are a personal choice. The Phenom is my personal favorite, so I've got one of them on four of my bikes.

3. Crank Brothers pedals -- All of my bikes have some model of Crank Brother pedals. Mostly this is so that I don't have to different shoes for different bikes, but I like the pedals a lot too.

4. Shimano hubs -- All but one of my bikes have wheels that I built myself. The first pair I built used SRAM hubs, which are still spinning great after 7500 miles, but the quality of Shimano hubs relative to their cost has won me over.

5. Topeak MTX racks -- Like the CB pedals, this is as much about standardization as anything. I like being able to have one go-to bag that I can easily mount to any bike. While it's true that MTX is one of the few (if not the only) proprietary mounting systems and nearly all other bags mount to all racks, the MTX system adds enough convenience that after the first one I tried I ended up replacing all of my other racks with MTX models.

6. Niterider headlight bracket -- The nice thing about a self-contained rechargeable light is that it's easy to move between bikes. Twelve dollars or so for a second mounting bracket and I've got great lighting for a second bike. All of the bikes I ride during the dark months (why does DST end???) have their own headlight bracket.

CharlieFree

Me too for both of these.

Also, my Deuter front triangle frame bag. I put my access card to access the bike room and keys for my lock in there. Quick, easy access. I have one on both summer and winter commuter bikes.

Todzilla

My glasses mounted rear view mirror.

Indispensable.

tjspiel

Though not really a cycling accessory I got it with commuting in mind. I'm a software developer that works with a variety of different tools and environments. While some people use a USB stick or some sort of Cloud service to access their stuff if they need to work away from the office, that has never been a successful approach for me. My laptop has a crap load of stuff installed on it along with a few virtual machines and it's changing all the time. It's just easier to bring it with me.

So one of my favorite accessories is an Incase "Sling Sleeve Deluxe". It's a laptop sleeve with a little more padding, a couple of pockets, some handles, and an optional shoulder strap. It allows me to safely carry my laptop in a backpack, pannier, or messenger bag without taking up too much room.

With the shoulder strap I can also use it on its own to carry the laptop while not on a bike. There's enough room in it for a few documents, earbuds, A/C charger, and a few other odds and ends. It's also "Airport Security Friendly" meaning that I often can get away with leaving the laptop in the case while going through the TSA line (not always though).

HardyWeinberg

zacster

1) Shimano hub dynamo and B&M Cyo Premium light
2) Magnic light rear light, contactless self generating light.
3) Fenders
4) Shimano XT 10sp drive train. I didn't appreciate how much things had improved until I installed this. Those that say the 6/7 speed of old was good enough are kidding themselves. It isn't the number of gears, its the smoothness of the shifts and the light touch.
5) My Knog messenger bag that has an attachment so that it is used as a pannier. I use it as my every day bag even when I'm not riding.

Wolf Dust

Paul Thumbies for converting Shimano bar end shifters to top mount thumb shifters. Also the Paul Chain Keeper for running a single ring up front with multiple gears in back. Two great products!

Oh yeah, and how could I have forgotten...Kool Stop brake shoes for my canti brakes! Won't use any other brake pad/shoe.

wsgts

Ortlieb Veloshopper - carries groceries and/or clean office attire.
Ortlieb Medium Office Bag - all the executive essentials, goes back and forth everyday.