Achieving large format colour feel

I'm guessing that by messing with selective hue/saturation etc you can achieve a similar feel to large/medium format?

You won't -- in large format film, there is lots of information and details. In large prints of dSLR files, much of the area is simulated information, so it looks both perfectly colored and yet amazingly lifeless...

Have you tried stitching? One of the main factors in the large format "look" is high resolution coupled with smooth tonality from having a large negative. Stitching a lot of shots together will produce a very similar result from my experience (I used to shoot 4x5 slide film).

Are you shooting full frame? If you are shooting a cropped sensor digital, how about going half way and getting a film MF camera? Properly exposed and well scanned, the enlarged prints would be quite a bit better than the average dslr.

The depth of colour in a 4x5 Velvia 50 transparency is breathtaking, when compared to identical images taken with 120 Velvia 50 and 35mm Velvia 50, on a lightbox. I only have a couple of cibachromes from 120 Velvia and only a couple of large prints from 4x5 negatives, but I have finally gotten into that range by stitching shifted images from a 5D II and 17 TS-E. The stitched files are in the same realm as current medium format digital backs.

Yes, post processing helps a lot too! Colour balance must be adjusted first since I have not had a DSLR yet that can consistently nail the correct white balance whether in auto, manual or matched to a white scene shot. I start by adjusting the white balance in PS raw converter, and then fine tune with colour balance in PS with the TIFF file. Then, since I primarily shot with high contrast saturated films like K25, K64, Velvia 50, Ektachrome 100VS, and Ektar 25, I saturate the image but generally colour by colour to get the results I want. Then I increase contrast very moderately so as to not lose too much detail.

@Mike Earussi
I haven't tryed stitching but I wan't to; I've been shown a very usefull technique whereby you use a tilt-shift lense portrait way up and shift it along from the same position 3 times ie. left middle and right and then you can achieve a seemless stitch and a huge digital file to work with. The only troulble is I don't have a tilt-shift lens :(
@Starvy Goodfellows
Yes i'm shooting full-frame for a landscape project I'm doing using a Nikon D3X (not mine, i'm a student and rent it out for free from uni) I just need a wide angle tilt-shift lens.

@John Crowe
That would be my ideal set up; a 5D II and 17 TS-E, but I just can't afford it atm.

ROFLMAO! I needed that. Thanks!

The problem here is that capture area matters. A small sensor isn't going to capture what a large sheet of film can capture. That's just the laws of physics talking to ya.

An example. Set up a 5x4 view camera next to a 5DMkII. Pick lenses so you have the same angle of view. Make your photographs. When you look at that telephone pole in the distance, you see that the digital picture is only 4 pixels wide. How much gradation will that yield in your final print? When you scan the 5x4 film (pick a reasonable scan resolution, say 4000 ppi, or even 2000 ppi) you'll find that the telephone pole is represented by many more pixels. So it's got much better gradation in the final print.

This is why people go though the pain and effort to use a view camera in the first place. And it's not something you're going to duplicate with a DSLR no matter how desperate you are to achieve it. I wish it weren't so -- I get tired lugging my 17Kg of LF camera kit up the mountain. But that's the price of image quality.

My suggestion would be to shoot some film side by side to begin with so you get a feel for what the film and digital differences are. Get a 35mm or cheap MF (mamiya C220?). However, I'm presuming you mean velvia 50 so here's a few starters.
1) Blue tone in the shadows - add a luminosity mask and add blue and remove a little red
2) use the saturation tool in photoshop and make a hue shift from greeny yellows and shift them toward blue
3) use the saturation tooll to make a hue shift of yellow/orange and shift them toward red.
4) You want to add a lot of contrast but doing so will darken parts of the image and lighten others. I don't like using highlight recovery (it always looks ugly) so I tend to darken the whole image using an aggresive curve and then use shadow/highlight tool to lift the shadows..
Finally, maybe use a bit of additional saturation - but try your hardest to add saturation by using contrast curves first instead of using the saturation slider. Most of the pop of transparency film comes from capturing images which only span a small dynamic range. These then look natural on paper. taking a picture with a large dynamic range and then trying to compress it will not.
Also I would advise you to buy a Sony A900 or Nikon D700 as their sensors look more film like whereas Canon senors have real problems with Chlorophyll