Online database of data sheets that isn't horrible?
The others have made great recommendations.  I'll add one small google hack that I use a lot:

[part number] datasheet filetype:pdf

So let's say you're looking for the LM629 datasheet... you'll google

LM629 datasheet filetype:pdf


or maybe an 74LS04:

74LS04 datasheet filetype:pdf


This has always worked well for me, since I know that the datasheets are going to be in the PDF format.