I've been reading a lot about "cross bikes" lately, and I've come to the conclusion that one would be perfect for me to ride to work on. I essentially want a road bike that I can jump gutters on and ride on some dirt/gravel tracks.

What sort of wheelset should I be looking for? Do people just get road wheelsets and run knobbly tyres on them? Or should I be looking at a completely different wheelset? They aren't going to be taking a major beating, so I don't need something that is incredibly strong, just enough to take the wider tyre really..

Look for a set of touring wheels, they'll be able to take a wider commuter tire easily and will be stronger for commuting. You could also consider a 29er wheelset and run cross tires instead of MTB tires. I use a Gary Fisher Utopia for my commuter - it came with Deore disc hubs and WTB rims - works great with a 42mm tire for dirt roads and bike path/urban riding. If you have v-brakes or road/canti brakes you will need a conventional rim, but the discs are nice for all weather riding if your frame and fork will accept discs.

I just put a set of Cane Creek Strados 700c Disc wheels on my 26" XC bike.($275 @ Cane Creek) These are narrow rims, Max tire 40mm per CC. On my Sofftail which had 26X2.2 slicks,with the CC's the biggest tire that would fit without metal work was 28mm wide(barely). Other bikes might do much better. The deep section aero type rims give the appearance from the side of bigger tires. These are rim brake compatible, Mavic says they have a 26"-700c rim brake converter (for their Speed City rims) but I've got discs so I don't know much about it.
Cheaper than buying another bike.

KHS Team Issue ST, Rockshox SID,BB7, etc.,etc.

Yeah, basically any heavy-duty set of road wheels will do. Make sure the rim is wide enough to support the size tire you want to run. As noted, 29er wheelsets will also work, assuming the rear dropout spacing is correct.

I would just make sure you run wheels with a good spoke count(32 or 36). For some reason a lot of the race oriented cross bikes come with pretty low spoke count wheels.

The low spoke count typically comes on wheels with straight pull spokes-no j bend. Supposedly they can tension them more so the wheel will be supported with fewer spokes. On the CC wheels the nipple is at the inside, so the rim is drilled with a very small hole, leaving more metal. Mavic uses specail alloys to make their rims stronger, the extra depth of the Cane Creek rims adds strength and spoke angle too. I'm not saying these are as stong as Rhynolites, but for commuting with street tires thay're probably OK. Mavic uses 24 spokes typically, CC uses 28 on their disc wheels.
Just remember that a 28mm 700c is the same diameter as a 2.35 down hill tire. If you're
going to run small tires then jumping, and hitting curbs isn't going to work for you anyway.
If you need to do this then get a 29er with Big Apples and Rhynolites (and lots of spokes)

salsa delgado X cross wheels. i've seen them survive ridiculous riding, and they're light.

double whoops

I am interested to read about "cross bike"

salsa delgado X cross wheels. i've seen them survive ridiculous riding, and they're light.

I second this. I'm running Salsa Delgados laced to XT hubs on my Crosscheck and use it for commuting, road riding, gravel grinders and hopefully crossracing. Wheels are stiff and seem sturdy.

Well in the end I decided to cop out and just go with 23c tyres. I'll ride around the dirt on my commute route (although some of the roads I'll have to ride on just plain suck!)

I have Planet X DN6's - "nice tough road rim for cross or 29er use" according to On One.

We'll see. :)

The next challenge is to see how long I can ride a SS to work. Honestly my commute is not the best. If it doesn't work out I am thinking of an internally geared rear hub, I'm just hoping in the mean time someone comes out with a shifter that will suit drop bars!

If you can't afford the mighty Rohloff 14 speed hub, Shimano has an upgraded version of the Nexus 8 with roller bearings that supposed to be much more efficient than the regular Nexus (which sucks up a little power all the time, my wife has one). I think Sheldon brown sells an adaptor for the Rohloff gripshift for drop bars-it probably would work for other gripshifts too.

I wonder what this would be like..?

http://www.mittelmeyer.de/html/rennlenker.htm

Also, I was thinking of a Sturmey Archer hub. The three speeds are very cheap, but I think a 5 speed is the way to go for me..

I run a stock Cross Check set up with Ritchey Speed Max tires. When weather cooperates I commute 120 miles a week. No problem once I understood the physics of a snake bite. Then I just went to a heavier walled tube.

I am interested to read about "cross bike"

Do a search "cyclocross"

My Felt F1X (Felt's CX bike) came stock with Mavic CXP-22 rims, DT Doubled Butted Champion Spokes and Felt Precision Sealed-Bearing Hubs. They are 32 spoke on both ends. I have hit a pothole at 33mph and straight into a 3" curb at 15mph, not to mention lots of other riding. They haven't even needed truing. The CXP-22 rims hold up to a lot.

EDIT - I see you are looking to fit a larger tire and not looking for something super strong. All I can say is that my bike came stock with 700x35 Kenda tires.