Any recommendations will be appreciated. I like The Lords of the Underworld series and The Dark Hunter series but I'm looking for something more in the sci-fi genre rather then fantasy. More along the lines of something futuristic or space travel or something not so much time travel if its mainly about the past.

Thanks in advance

Try The League series by Sherrilyn Kenyon. That's the only sci-fi romance I've read so far..

A lot of Sci-fi romance seems to fall into 'teen' fiction.
The Lunar Chronicles by Marissa Meyer is an engaging series.
The Pledge series by Kimberly Derting has a really interesting world.

Try the Alien series by Gini Koch. They're really good books.

Definitely agree you should check out Gini Koch's Kitty Katt series.

Also recommend Lois McMaster Bujold's Vorkosigan saga.

And Sharon Shinn's Samaria series. Though it may not seem like sci-fi at first.

Psy-Changeling series by Nalini Singh
New Species by Laurann Dohner
Lux by Jennifer L. Armentrout (It may be more YA :/ but great series)
Katherine "Kitty" Katt series by Gini Koch
Breeds by Lora Leigh
Aurora Rising by G.S. Jennsen
Tales of an Extraordinary Girl series Showalter Gena
Age of X by Richelle Mead

Enjoy

Catherine Asaro's Skolian Empire series.
It's more sci-fi than romance, especially the middle books, but the world building is exceptional. She's won a few prizes for these stories IIRC

Try the Theirs Not to Reason Why series. The romance only starts up later on (the second book I think) but the entire series is great.

[sevenseeds]

One of my FAVORITE sci-fi romance series is the Alien Affairs series by Katherine Allred. I love it because it isn't erotica, which I've run into a lot in this genre, but at the same time, it isn't so focused on the technical aspects that so often cause romance to take a backseat in sci-fi fiction. The plot is really good, the characters are well-formed and believable, and I think the author has some creative ideas that make a future in space seem realistic yet at the same time enchanting.

Try Paradox series by Rachel Bach. It's a slow burn like Sirantha Jax series by Ann Aguirre. Also an Ilona Andrews short titled Alpha. It's in an anthology.

In Her Name series by Michael R. Hicks superb series with great plot line and well woven story line.

https://www.goodreads.com/author/show/1713558.Michael_R_Hicks

The Dragon Lords of Valdier by S.E Smith
New Species by Laurann Dohner
Psy-Changeling by Nalini Singh
Tornians by M.K Eidem

Celta series by Robin Owens

Very good series IMO - especially the first 2 or 3

[Victoriana]

All books by Linnea Sinclair are sf romance

[krazny9]

I second the Vorkosigan Saga by Lois McMaster Bujold recommendation.
I'd also recommend Connie Willis' series starting with Blackout.
Diana Gabaldon's Outlander series is also quite good. It starts with Outlander and goes on for a bit, so enough to sink your teeth into.