Here's a concept that I've been thinking around over the past few weeks: an Imperial Guard Ally detachment for deepstriking armies.
The idea is to use the Imperial Guard specifically as a way in which to augment a fully (or mostly) deepstriking armylist such as Death Wing, Daemons, and the like. It revolves around manipulating the reserve roll: taking options like the astropath to improve early, rapid deployment.
Here's one option:
Company Command Squad, 1 Astropath, 1 Officer of the Fleet (110 points)
1 Veteran Squad (70 points)
Aegis Defence Line, 1 Communications Relay (70 points)
Total = 250 points.
Now, combine with your favourite (e.g.) daemons list and you have a 35 in 36 chance that all your units will be on the board on turn 2. The Officer of the Fleet is there to oppose enemy deepstrikes so that your own army can take down the enemy piecemeal if they're employing a similar army. Deploy somewhere out of sight (perhaps even add a Chimera) and behind the defence line to control communications array and keep them there until the start of turn 2. Then redeploy and engage as required.
At 250 points, it might not be so worthwhile in a 1500 points total army, but at greater points, I think it would be invaluable.