Personally, I don't really like the automatic crop marks Illustrator creates, and if you're sending these business cards to a printer, I would suggest talking to them first to see if you need to arrange your file this way at all. There's nothing worse that designers doing a printer's job, and then the printer having to undo all that work because they have imposition software that does it all anyway!
Anyway, if you do have to create a file like this, here are a few pointers. Try to be as accurate as possible.
First step is to set up one business card correctly, with an even amount of bleed around it (even if it doesn't have any bleed).
1: Create one business card correctly.
2: Create one horizontal and one vertical guideline near the edge of the page, and line up the corner of the business card to that.
3: If your business card bleeds off the edge, make sure that the bleed area crosses the guidelines - the guides represent cuts for now.
4: Draw a rectangle the same size as your business card + the bleed area. For example, if your card is 85mm x 55mm, and you need 2mm bleed on each side, draw the rectangle 89mm x 59mm.
5: Position that rectangle so that it crosses the guides by exactly the bleed amount. It helps to set the origin to the intersection of the guides so you can use the transform palette to position it accurately.
6: Select All, and go to Object > Clipping Mask > Make.
Now you have one business card with bleed. The next step involves duplicating it and adding the cut marks. It's important to realise that you rarely put just one crop mark between two cards. In general, you have a card, a crop mark, bleed from card 1, bleed from card 2, then the second card. If you don't, the cut won't be as clean, and if there is bleed, you might have part of card 2 showing up on card 1. For example, if you're doing 2 across and 5 down:
1. Select All, then go to Object > Transform > Move...
2. Set Horizontal to the width of your card + bleed (eg 85+2+2 = 89mm) and Vertical to 0. Press Copy.
3. Select All again, and go to Object > Transform > Move...
4. Set Vertical to the height of your card + bleed (eg 55+2+2 59mm) and Horizontal to 0. Press Copy.
5. Keep pressing Object > Transform > Transform Again to keep copying until your page is filled. Better still, use the keyboard shortcut.
Now add the crop marks:
1. Create a new layer.
2. Draw a horizontal line along the horizontal guideline, extending from beyond the image area on both sides.
3. Object > Transform > Move... and set Horizontal to 0 and Vertical to the height of the card without bleed. Press Copy.
4. Now select both lines and Object > Transform > Move..., this time setting Vertical to the height of the card with bleed. Press Copy, and using Transform Again until all the rows are marked with lines.
5. Repeat the above process with Vertical lines.
6. Draw a white rectangle starting at the top left bleed area of the top left card, and cover all the cards and bleed completely, so only the cut marks are visible.
7. In the layers palette, drag the layer with the cut marks to the bottom.
That should be it. Sorry if it sounds overly complicated - you'll find shortcuts as you go along. I tend to deal with designers everyday that take the wrong shortcuts, and it does nothing but delay their jobs!