Commuting - Pannier suggestions and recommendations

Now that I've started commuting on a more regular basis, I'm thinking about getting a set of panniers. I'm keen to move myself to a situation where I don't need the car, which means I need to be able to carry the following:

Laptop (+power supply, mouse)
PDA
Clothing for the day (shirt, pants, socks, underwear)
Small towel + deodorant
Lunch and occasional snack top-ups
Wind/rain jacket
Personal bits & pieces (e.g. cell phone, wallet)

I leave shoes at the office. In the winter I leave a sweater and a jacket at the office. Bike spares are already taken care of in a seat pack, which I'll keep doing as it means I can jump on the bike without the panniers and still have flats etc covered.

A secure mounting system and strong construction are my primary concerns. I don't want to go overboard with price, but am not necessarily on a tight budget. Waterproofing would be nice, but given how infrequent the rain is in Denver this isn't paramount - I'd be happy enough using plastic bags inside, I think. I'll likely get a Blackburn Expedition rack. For the short term the rack/panniers will be mounted on my Giant Farrago, but this will soon be replaced (possibly with a Soma Doublecross, not sure yet - but either a light-touring or non-competition cyclocross bike).

The options that look good for dedicated laptop carrying are the Carradice Bike Bureau (http://www.sheldonbrown.com/harris/bags/city-rider.html) or Arkel Briefcase (http://www.panniers.com/panniers/briefcase/overview.asp?site=). Has anyone used these? I'm assuming it might be a tight fit to use either of these for carrying the computer and associated paraphernalia as well as clothing and clean-up stuff.

It's not essential that I have an actual briefcase-style bag for the laptop carrying. Has anyone used standard panniers for carrying a laptop? If so, which ones? I was interested in something along the lines of the Arkel T-42s (http://www.panniers.com/panniers/t42/overview.asp?site=), which seem to be a good size. The appeal here is that these panniers are a bit less bulky, and I can carry the laptop in the non-traffic-side pannier, and even leave that pannier at the office when I don't need to take my laptop home. It also would give me better panniers for some light touring in the future.

Sorry for the long post... any opinions or suggestions would be welcome! :D

I went with the Arkel T-42s and have been happy with them. Rugged and spacious. I don't even bother with the lock system--just hook the bungee hook and the top hooks onto the rack for my 10 mile flatland ride. Like you say, computer in one, gear in the other. I already had a padded computer bag that luckily fits exactly inside the t-42--I put its shoulder strap on the arkel bag when I don't want to carry everything in my hands.

I use Nashbar panniers. Rain/weather gear in one, daily clothing in the other. Shoes left at work too. When I have to take my laptop (IBM A20m ThinkPad) back and forth I bungie it to the top of my rack in its padded case. Have had no problems.

The Carradice has a clip-on fitting which is much quicker than fiddling around with bungie hooks.
Maybe you should get a 2nd power supply for your laptop.

The Arkel briefcase is absolutely fantastic, there is no comparison to it for a bike orientated laptop pannier. I've used mine for over a year now and I really can't say enough good about it. Except that they have actually improved it with a new version for this year (I got to check it out at the Seattle Bike expo) Apart from my laptop which is a 15" Powerbook that completely fits in the sleeve, I keep my lunch, PDA, power supply and misc books or CD's in it. You could put more into it, but probably not bulky stuff like clothes. As I do carry other bulky stiff I use a second pannier on the other side. I use an old Jandd pannier that i have had for about a decade now (tough bags) to carry a thermos, rain gear, etc. This is pretty small (a little smaller even then the Arkel GT-30's I use on the front rack for tours) I prefer the balance of having both panniers on the rear and this is a good combo.

I use Nashbar panniers. Rain/weather gear in one, daily clothing in the other. Shoes left at work too. When I have to take my laptop (IBM A20m ThinkPad) back and forth I bungie it to the top of my rack in its padded case. Have had no problems.
Thanks for the replies!

I'm thinking this is the option I'll go for, except with different panniers. I like the look of the Arkel T-42s - they seem the right size and strength for what I want to do (commuting and occasional weekend touring), and I'll just do as you suggested and transport the laptop in it's padded case bungied to the rack if it won't fit nicely in the pannier. Since a briefcase pannier is $100-150 and I'd need a normal pannier for clothing anyway, I think I'll try this out and get the briefcase pannier at a later date if I really need it. I'll only ever need to transport the laptop either before or after I fly somewhere, so its trips in the pannier should only be a couple per month.

I do actually own a second power supply which typically lives in the laptop bag so that it's there when I travel (the other is permanently at the office). I hadn't really thought about it, but of course the second one could just stay at home.

I use Ortlieb bags, a handlebar bag which also can hold food, maps, phone and other items, on the back rack I carry large pannier with clothes, shoes, etc on one side and a computer bag with padded insert, notebook PC, papers, etc on the other side. The bag is also a standard shoulder back when removed, and the pannier can be fitted to become backpack. The handlebar bag is also a shoulder bag. All these bags have quick release and security cables/lock option (if you want it) and are waterproof. Their bags are not inexpensive, but they sure are good.