The best needles to us for cross-stitch are tapestry needles. These needles are blunt and won't pierce your fabric. For up to 14 count fabric; use a size 24 needle. For 16 to 20 count fabric, use either a size 24 or 26 needle. For 22 count and higher, use a size 26 or 28 needle. The eye of each needle size is different, allowing for more or fewer floss strands. Just like with your fabric, the higher the number, the smaller the needle. The only time you would use a sharper needle is when you stitching through waste canvas to make a design on clothing or an accessory.
When you are stitching a large design, or one with several colours in one area, it will save time if you thread several needles with different floss colours. I use plastic bobbin cards for my floss, so each pre-threaded needle is stuck through the floss remaining on the card. Another method I have seen somewhere in my travels is to use a piece of magnet strip glued onto heavy cardstock. Write in pencil above the magnet what colour is in each magnet. When you are finished your design, simply erase the colours, and you can use it for your next project.
I have read in several places about not leaving your needle threaded through your fabric when not sewing. I have to admit that I am very guilty of doing that, and thus far haven't had any problems, but then I sew almost everyday, and the needle is never left in the same place for days on end. If you don't want to risk leaving your needle in the fabric, you can use a needle keeper or pincushion.
Two-Tipped Tapestry Needle
This needle is a fairly new commodity in the cross-stitch market. The eye of the needle is in the middle, and each end is a blunted point. The best thing about this needle is that you don't have to turn the needle as you stitch, which could cut down on RSI but they do take some getting used to. Partly because of the length, it is twice as long as a regular needle, partly because you are so used to turning your needle. You must remember to let your needle dangle often, so the thread untwists, otherwise you will have a large tangling problem. These needles are easier to use on a scroll frame rather than a handheld hoop.