network rack

Any cage will do.  If you're looking for an equipment rack, I'd recommend getting two (one for the front and one in the back to support the weight.  I'd never mount a Dell server in a two-post equipment rack.  As for recommendations they're everywhere.  Dell even sells cages.

Any cage will not do.

We ordered in the past and they were not deep enough.

Not sure what kind of depth you're looking for.  At both my current place of work and my last (Net Admin for both) I've mounted equipment ranging from Dell 2850, 2950, R510, 520, 610, 710, 720, and MD3000i & IBM i Series boxes in both Dell cages and a pair of two-post equipment racks without any issues.  We even had a couple cheapo Taiwanese knock-off cages in our Vegas office that help PE2850's and PE2950's without a problem; we just didn't use the Dell cable management arms in those particular cages.

Good luck.

Enclosed please.

I have just purchased a rack for Dell R630s amongst other devices.  It couldn't be longer than 1000mm, due to space constraints in the room where it is located.  1000mm deep doesn't allow space for the cable management arms as stated already.  1200mm is probably the deepest available, and what's required to fit those arms.

Regards width, that just down to your choice.  The rails are also the fixed 19" apart, but a wider rack may have cable trays running vertically to tidy up patching cables.

David,
Do you have a rack that will fit?

check craigslist
I have found short ones on there in the past

If you're looking for a new one then you're best option would be to either contact your server suppliers to see if they can provide the cabinet or most cabling (cat5e etc) distributors sell them so thats another option.

If you're looking for used then Craigslist or ebay are good bets.