Heat
I live in Arizona. The heat is of the brutal, searing type. I also ride every day. Rain, shine, or temperatures in the teens.*

Note this is 91º at 8am, later in the summer
it will be over 90º all night long!
My ride is only 3.5 miles, and only takes 10 minutes if I hit all the lights and average above 16mph, but I am still a sweaty mess when I get to work. There are no showers in the building, although there are some across campus. I usually don’t get out of the house until 7:40 so I have no time to stop and shower on the way in.
So what do I do? Am I wet and noisome all day? No, I have some tips for staying fresh year-round. The key is in the clothes and a few supplies.
Part 1: the Clothes
Let’s start with what you wear while riding to work. For pants, I have some of those meshy, basketball-type drawstring shorts. If you commute is more than 10 miles, I would invest in some bike shorts. If you have an aversion to showing your goods in public, the bike-short undershorts are good too, or you can just wear shorts over your bike shorts. Keep in mind the heat factor here. Things get swampy quick.
Speaking of swampy, I have to talk about one of the greatest inventions of the modern age — Under Armor. This underwear makes you feel like an NFL astronaut. Space-fricking-age materials keep you cool in the most moist of nether regions. They ain’t cheap, but once you go there, you will never wear anything else. The “HeatGear Boxerjock”® make fantastic ersatz bike shorts. But only use as underwear, not shorts, which I may or may not do in the early morning on Sunday while doing yard work.

Actual photo of me, my ripped abs, my package, and my massive veiny arms
T-shirts are good to ride in, bike jerseys are better, and the poly-spandex athletic performance shirts are best. Bike jerseys can be pricey, but you can find athletic shirts at a discount outlet (Ross) for about ten clams. The loose t-shirt style are preferred over the spandex-bodybuilder style for ventilation and summer comfort. (and not looking like a douche)
Socks are another thing to consider for heat and comfort. Thin socks to ride in, dress socks at work, and if it is a really hot day you can change your dress socks at lunchtime to a fresh pair which can help restart your mojo. As for shoes, sandals may seem like a good idea but sunburn and road rash are an issue. Also if you have not discovered clipless pedals, you are definitely creating more work for yourself, and creating more sweat!
I keep a belt and shoes in my office. Two reasons: I don’t need to haul them back and forth every day which would be more effort, and they are always there. (I hate forgetting a belt and having to tug at your pants all day) I used to keep a pair of pants, socks and a shirt in the office in case I forgot one of those items, but I stopped doing that after a year or so.
So that leaves very little to carry to work — socks, pants and a shirt. The shirt and socks are rolled up in the pants for easy transport. Just make sure your lunch is sealed tight so you do not leak last night’s leftovers onto your new pants. (never happened to me, really)
Don’t put those work clothes on just yet! There are a few more things to attend to once you are in the office. I will cover that in part 2: transition tips.
Editors note: I just noticed this is a very male-centric post. I cannot speak for the ladies, but if you are one and would like to contribute, please comment below.
*teens in AZ = over 112º f