Or at least more appealing. I've been looking at allies for my Blood Angels recently. I guess it's down to that whole "oooh shiny" approach to things where new stuff always looks nicer. I did pick up an Eldar Codex from eBay to see what my options are, however I think it's more likely that I would use this to start a new army some day, as I suspect the points would be better spent on more Blood Angels.
On a similar theme I re-discovered my stash of Orks that I've had for about 3 years. I totalled up the points and I have about 750, in an unpainted state. Not bad. I think I still have the codex for it but it's packed away in storage until we move (hopefully soon now I have a job). So I think it would be best to concentrate on this for an alt army. It's not ideal as they are a close combat army much like the Blood Angels but with more bodies and less armour. Still I've always liked the custom and conversion aspect of creating an ork army, and my best successes were with Orks in 3rd edition. Mind you in those games it wasn't so much tactical genius as "how many Orks can we get into close combat as soon as possible?"
Still with the new flyers it could be interesting. I still like the look of Necrons and miss my BattleFleet Gothic Necron fleet. Yes they are a bit overpowered in 6th edition and everyone and their dog seems to be fielding some but the fluff is quite fun. Same with Tau, although they desperately need a new codex. I doubt I will collecting a new army for quite some time tho, due to finance etc.