There are a few fundamental sites that carry very good information about minis from the old days.
• Stuff of Legends: - an easy to navigate basic bare bones site that will help with identification or reminiscing about older minis.
• Lost Minis Wiki: - just as easy to navigate, and featuring some more detailed images on some items than Stuff of Legends. I tend to favor this site when looking for confirmation/identification of Grenadier minis (but they cover many companies).
• DnDLead: - Nice enthusiastic site with many nice photos of painted minis.
For Citadel stuff there are some great images on dakkadakka, but you need to search the galleries. Lots of older minis but also pages from older White Dwarf issues.