At first we practise slow randori from grabs with such techniques as tenchi-nage, irimi-nage, kokyu nage where there is a requirement for a lot of blending - it is somewhat artificial at first but develops the idea of moving off centre line and positioning.
I know people have different theories on this, for safety reasons, but I prefer people to throw the uke at other attackers - it is for the other ukes to move out of the way and stand up quickly so they don't get someone thrown on top of them.
We generally have 2 styles of randori. The line of 4 people in front, where the intension is to go to the edge (being very pro-active) and pick off that attacker, throwing them in to the others so you always keep the attackers in front of you (unless you are specifically setting the person behind you up). The other is a circle, but the principle is the same - to get out of the circle (by throwing someone from the edge inwards) and have your attackers in front of you. The point of out multiple attack is that everyone should attack you as soon as they can, and if two people can attack you at once you are doing it wrong.
When people are happy with blending I think it is actually much easier to have freestyle defence (from set attacks), this helps you control uke and is more realistic because it is difficult to force a technique on an uke who is reacting very differently to what you expect.
The best is free style attack and defence, though being able to change techniques and move quickly is essential - I've never tried randori with weapons but I expect it is immensely difficult and probably quite dangerous.
P.S. thanks for the new ideas Matt & Anne - I'll give them a try (though I have enough trouble tripping over ukes with my eyes open)!
[Edited by ian on February 20, 2001 at 06:42am]