Currently Online 
I know a lot of old games that a very good.
Septtera Core
It's an RPG, the world is made up of flying continents that are situated at different altitudes. The combat is real-time, sort of, each character, you can have three in a battle, has a little circle that fills during the battle, depending how full it is you can use different attacks, there are also some cards you can use that have different abilities from direct damage to healing, and if they are used in combinations you can achieve spectacular results.
It plays faster than shown in the video.
You can buy it from GoG.com for $5.99.
Titan Quest series
They are similar to Diablo in game-play, but they don't have the annoying identify items and you can generate a portal anywhere to get back to a town. They are set in Greek mythology.
You can find on several DD stores, and maybe in physical stores.
The Elder Scrolls series
I've only played Morrowind. They are WRPGs with a big overworld, it could take hundreds of hours to do all the quests and go through every dungeon.
Steam is having a sale today on The Elder Scrolls IV: Oblivion® Game of the Year Edition Deluxe.
SpellForce series
RTS/RPG hybrid series. I will mainly talk about the first game in the series, you play as a Rune warrior which are people who have had their souls sealed in a rune. The main characters can level up, but the up to 5 additional characters you can have are chosen from ones that are at a fixed level and you can swap them out. Most maps are RTS, while some are like dungeons in Diablo.
Several DD stores have them.
Freedom Force series
It is an RPG series, in a way. You have 4 heroes in a mission, you can choose from a high number of pre-made heroes or you can make your own.
Again they can be found cheap on DD stores.
Star Wars: Knights of the Old Republic
I don't think I have to describe this one.
Aquaria
It's a Metroidvania platform under water.
It's on Steam for $20.
I know some others I'll list them later.
