A few weeks ago, this was the extent of my collection.......
Now it's grown somewhat -
L > R
Blue & Red "Powerlight" 1xAA http://www.focalprice.com/detail_LF601L.html http://www.focalprice.com/detail_LF601R.html
Grey & Black Sipik SK58 1xAA / 14500 http://www.focalprice.com/detail_LF554X.html http://www.focalprice.com/detail_LF550B.html
Grey & Black Sipik SK68 1xAA / 14500 http://www.dealextreme.com/details.dx/sku.39584 http://www.dealextreme.com/details.dx/sku.39585
Romisen RC-G2 1xAA http://www.focalprice.com/detail_LF013B.html
Romisen RC-29 1xAA http://www.ledshoppe.com/Product/ledp/LP1084.htm
C78 1xAA / 14500 http://www.dealextreme.com/details.dx/sku.29095
X2000 1x18650 http://www.dealextreme.com/details.dx/sku.14450
Ultrafire C28 1x18650 from ebay
2 x 4D Maglites from ebay
I thought I'd share a few thoughts on these for anyone interested
Blue & Red "Powerlight" 1xAA fixed beam
I must admit I was expecting these to be brighter. I first turned them on at daytime and could barely see the beam on something a metre or so away indoors. However at night time they are a usable light if you just want to see where you're going or what you're doing. Effective range is about 5 metres up to about 10. Best thing about these is the price - under $3. They seem to be fairly well made (for the price) and look quite good.
Grey & Black Sipik SK58 1xAA / 14500 focusable beam
A lot brighter than the powerlights obviously, but still not very bright. Build quality is OK although the head has a rough feel to it when you slide it to focus the beam. They don't look too bad I guess, not a fan of the bulky lanyard it comes with though. For $6 or less you can't really complain, but I don't think I'll be buying any more of these.
Grey & Black Sipik SK68 1xAA / 14500 focusable beam
These are a nice bright light and can take a 14500 battery, build quality is OK, the clips on these particular ones aren't too bad, however previously I bought some and the clips were very dodgy. Any pressure whatsoever on the clip and the threads would just let go. The head feels a bit rough when sliding, same as the SK58. For $9 these are pretty good performance wise I reckon, but ugly in appearance.
Romisen RC-G2 1xAA fixed beam
I love this thing, build quality is excellent and looks good too. Only thing is it's noticably less bright then either the SK68 or the C78. I guess battery life will be better though. Can't take a 14500 unfortunately.
Romisen RC-29 1xAA focusable beam
Again, excellent build quality, but definately not as bright as some of the others. Not sure if I like the look of this thing or not. I guess it's OK apart from the tailcap. This is the only one out of these with twist focus, push-pull focus is lot faster, but twist focus is smooth and means the head doesn't rattle, unlike the others. As with the RC-G2, it takes AA's only
C78 1xAA / 14500 focusable beam
This is brightest out of all of them, and can take a 14500 which makes it even brighter still. Build quality is OK except for the switch which is rubbish - it's loose and jams up regularly. If this light had a better switch I would say it'd be the pick of the bunch.
Be warned that Focalprice and probably other places sell a very similar (in appearance) version of these - DO NOT buy these ones as they are absolute crap! The switch is even worse than the "real" version and they're not much brighter than the powerlight. http://www.focalprice.com/detail_LF602B.html
X2000 1x18650 focusable beam
Works well, looks a bit bland, acceptable build quality. Nice and bright but not quite as bright as the C78, flood is better though. A decent light but not very exciting (too me anyway)
Ultrafire C28 1x18650 fixed beam
Nice light, OK build quality, but again, nothing to get too excited about though. I have another one of these mounted to a riflescope and it works well.
4D Maglites
I only got these today and haven't used them yet as I haven't got D size batteries at the moment. I bought these secondhand on ebay for under $50 for both of them and plan on modding them, but haven't decided how just yet.
Summary:
Cheapest - Powerlight
Brightest - C78
Best build quality - either of the Romisens
Best all round? No clear winner, in my opinion!
Cheers, Dave.